Imported from GitHub PR https://github.com/abseil/abseil-cpp/pull/1412

In Clang, an `-Xarch_` compiler flag indicates that its successor only applies to the specified platform (e.g., `-Xarch_x86_64 -maes`). This is used in `absl/copts/AbseilConfigureCopts.cmake` to selectively enable hardware AES support on Apple platforms.

However, when generating pkg-config files, those `-m` flags are filtered out, while the `-Xarch_` flags that precede them are left untouched. This led to the error reported in #1408.

Fix that by filtering out each `-Xarch_` flag with its successor at once.

Fixes #1408.
Merge 89d20ab816b7cead56f05d5a6bc5146d1c4f4335 into 34604d5b

Merging this change closes #1412

COPYBARA_INTEGRATE_REVIEW=https://github.com/abseil/abseil-cpp/pull/1412 from ZhongRuoyu:xarch-pkgconfig 89d20ab816b7cead56f05d5a6bc5146d1c4f4335
PiperOrigin-RevId: 606730193
Change-Id: I3e177a56721acd3145fd03c64102741898afd2a5

This function copies the parser's state onto the stack in order to perform backtracking.
Adding a complexity guard will ensure that it fails gracefully, instead of contributing to excessive consumption of stack space.

PiperOrigin-RevId: 606720511
Change-Id: I2f6f03e5f8bc4cc571a4159ecfc2af6f3e00fa68

absl::kuint128max should be replaced with absl::Uint128Max()
PiperOrigin-RevId: 606279299
Change-Id: Ib67b5431f14891f56bb706e62f183d0de75d335f

This allows us to annotate nontrivial types that should be flagged as unused
variables.  Compilers otherwise ignore nontrivial variables as their
constructors/destructors may be desired and intentional (for example, a scoped
lock).

PiperOrigin-RevId: 606266618
Change-Id: I64b5f6d32a3cec2f18e0aa9029905f5e836c11a9

For example, this covers the following:
```
template <typename T>
    requires std::integral<T>
int foo();
```

Refactor parsing of `Q <requires-clause expr>` into a single function that performs backtracking to avoid reimplementing `ParseTemplateArgs` in terms of nested if-else blocks.

PiperOrigin-RevId: 605785418
Change-Id: I118998a75e050dcf46af125b613b690312fd3cbe

The Apple implementation gives false positives starting with
Xcode 15.

PiperOrigin-RevId: 605726702
Change-Id: I2e5e574eca08071d24e97304f005cf9c78230913

These clauses show up in other places that end up mangled as parts of function signatures (e.g. on template struct params). We'll handle those in a follow-up.

PiperOrigin-RevId: 605694497
Change-Id: I1bfe4c0cfaa739fdd24548b1547482410c92b5a7

PiperOrigin-RevId: 605460827
Change-Id: I57007a7ad18829e7bfed27ba65871afbd227d012

`demangle`: Parse C++20-compatible template param declarations, except those with `requires` expressions

Support for `requires` expressions will be added in a follow-up.

PiperOrigin-RevId: 605418370
Change-Id: I2c84cdf0c4599e36683b3c94dcbb173ab4fc3ee8

This macro is used by a Google-internal service for automated
refactoring. It is being released so that Google projects that
use this service can also open-source their code that uses it.

PiperOrigin-RevId: 605322286
Change-Id: I16babcc56c454e07461690a8bb58be5da72d283f

PiperOrigin-RevId: 605288522
Change-Id: Id16ad96b9323c71bd60801a6c8c359f7ff3d320e

PiperOrigin-RevId: 605125821
Change-Id: I2ee260eaf283acafd80abfd2b7419a0e9f597a78

Avoid hash computation and `Group::Match` in small tables copy and use `IterateOverFullSlots` for iterating for all tables.

PiperOrigin-RevId: 605116090
Change-Id: Ia65c664421f7630225b00f1c45c636b4681121ce

Throughput of the 64 byte chunk loop inside `LowLevelHash` (or now in `LowLevelHashLenGt16`) gets limited by the loop carried dependency on `current_state`. By using 4 states instead of 2, we can reduce this duration by 1 cycle. On Skylake, it is reduced from 9 cycles to 8 cycles (12.5% faster asymptotically).

To see the reduction in a simplified version of `LowLevelHash` implementation on Skylake:
* Before: https://godbolt.org/z/Tcj9vsGax, llvm-mca (https://godbolt.org/z/3o78Msr63) shows 9 cycles / iteration.
* After: https://godbolt.org/z/q4GM4EjPr, llvm-mca (https://godbolt.org/z/W5d1KEMzq) shows 8 cycles / iteration.
* This CL is removing 1 xor (1 cycle) per iteration from the critical path.

A block for 32 byte chunk is also added.

Finally, just before returning, `Mix` is called 1 time instead of twice.

PiperOrigin-RevId: 605090653
Change-Id: Ib7517ebb8bef7484066cd14cf41a943953e93377

PiperOrigin-RevId: 605030710
Change-Id: Id273d0ff79ebff4f753a4ca9818e2b53661d6fee

`char_traits<>` implementation, recently removed from `libc++`.

PiperOrigin-RevId: 605023824
Change-Id: Ia708c91c24625afc4504fa77e959f8ed1e025589

SwissTable provides support for heterogeneous lookup in associative
containers through transparent Hash and Eq types. However, it is not
possible for user types to provide additional specializations to allow
their types to use this functionality.

This CL brings ability for user types to specify their own transparent
absl_container_hash and (optionally) absl_container_eq inner types to
achieve the same functionality.

PiperOrigin-RevId: 604994859
Change-Id: I302486d292c9a18b7d4c77033227008f5539e354

C++20 introduced constraints, where concepts such as `std::integral` can be used to restrict template parameters:

```
template <std::integral T>
int foo(T t);  // Only accepts integral types.
```

Clang mangles these starting with a prefix `Tk`, followed by the concept name, which mangles as a type.
For example, compare `foo` and `bar` here: https://godbolt.org/z/Kzbrrchde

Note that this implementation doesn't cover the more complex case where the concept is templated too. See [llvm's implementation](https://github.com/llvm/llvm-project/commit/4b163e343cfa54c8d55c9da73c70d58f55ea9df2) and its tests for a thorough version.

PiperOrigin-RevId: 604976260
Change-Id: Ic116c5f6f27c3f7714638bdee8de11dce871f0be

Roll forward 9d8588bf (which was rolled back in 146169f9) with fix.

PiperOrigin-RevId: 604534265
Change-Id: Ic70ae72d4d73ac8849196cb844c8de32790bd6c8

to validate that the input was actually valid hexadecimal data.

Mark the version of absl::HexStringToBytes() that does not validate
the input as deprecated.

Fixes #141

PiperOrigin-RevId: 604495678
Change-Id: Iac3020c33c9dbc6d8e31a43b746783fb345edaa7

PiperOrigin-RevId: 604369517
Change-Id: I6024a8828563c5a2487ba85ede91a88d7059f9c8

PiperOrigin-RevId: 604094890
Change-Id: If5634a15c7ea7c8ef2cc9b6d09636ee7836946d2

PiperOrigin-RevId: 603816996
Change-Id: Ifc7dc6299e65043697b4a0c6e9e8eef869297ce3

PiperOrigin-RevId: 603784442
Change-Id: I3d57e5f438b276c984f5d5416889b19e7ddb501a

PiperOrigin-RevId: 603696164
Change-Id: I876ae0ead5964b626c285c60d9a4b2bbe62e113d

PiperOrigin-RevId: 603576688
Change-Id: I5e7868de7016d76fb7a44fea93be72ab90f239d3

CycleClock::Now utilizes ABSL_INTERNAL_CYCLECLOCK_SHIFT to discourage reliance
on the raw CPU cycle counter values. As a side effect, it discourages
strictly-increasing assumption. Apply the idea to discourage over-reliance on
the precision of absl::Now/absl::GetCurrentTimeNanos.

Programs relying on a very high precision often exhibit portability issues on
machines with a lower cycle counter precision, or worse, race conditions. For
example, Apple M1 emulated x86 RDTSC only guarantees weakly-increasing RDTSC
values.

x86 clock speed is usually measured in GHz and is still precise after we drop 8
least significant bits.

PiperOrigin-RevId: 603493500
Change-Id: Ib1b00075109283f5dbcb39a43fe0ab722351a1e2

There are three optimizations here:
1. Early exit in case all slots were destroyed. especially useful for empty tables.
2. MatchFull is used in order to iterate over all full slots.
3. Portable group is used for `MatchFull` in the case of small table.

PiperOrigin-RevId: 603434899
Change-Id: I40bc90d17331d579cfbb1b4e0693f0913e5c38e4

PiperOrigin-RevId: 603344396
Change-Id: I06721246bf205284843065687378c6d905cbf879

PiperOrigin-RevId: 603342563
Change-Id: I1cd80103377f457770d5178dad8b56ae459cbd55

PiperOrigin-RevId: 603148301
Change-Id: Ie2e5702995c9e1ef4d5aaab23bc89a1eb5007a86

https://bazel.build/build/style-guide#other-conventions

PiperOrigin-RevId: 603084345
Change-Id: Ibd7c9573d820f88059d12c46ff82d7d322d002ae

PiperOrigin-RevId: 602974812
Change-Id: Ic35b41e321b9456a8ddd83470ee2eb07c51e3180

PiperOrigin-RevId: 602864815
Change-Id: I74db20c93f6a7d9046779677cb4a328dc54bae69

PiperOrigin-RevId: 602813933
Change-Id: I744fe438281755a141b2fd47e54ab9c6c0fad5a3

Closes #1536

PiperOrigin-RevId: 602764437
Change-Id: Ia5c20a3874262a2ddb8797f608af17d7e86dd6d6

Also updated the return value to reference to clarify non-nullability.

PiperOrigin-RevId: 602730828
Change-Id: Ia36f7fde3cc87ac597ba4f194eebe9ebb90a1a09

When bzlmod is enabled and WORKSPACE.bzlmod exists, the content of
WORKSPACE is ignored. This prevents bzlmod builds from unintentionally
depending on the WORKSPACE file.

This exposed some small problems with our clang-cl configuration,
which are also fixed in this change.

PiperOrigin-RevId: 602511311
Change-Id: I0ba411edde2df0e17f4eeede4117ddb6934dd8f8

PiperOrigin-RevId: 602485199
Change-Id: I5cc10eb8dcfe5988cf939080a224522e02ad8607

AbslHash allows for piecewise chunks to be streamed incrementally into hash states and requires them to hash identically to one giant stream.  The exact size window for this is an internal details `PiecewiseChunkSize`.  There was an off by one error in this code.  Add tests and fix it.

PiperOrigin-RevId: 602463183
Change-Id: I159bbb5e7e745f55b2fe6eaf0d2735bd0a08aca9