standardized in C++11
Migrate all Abseil code to `[[noreturn]]`. Notably,
https://github.com/abseil/abseil-cpp/issues/1698 reports that
`[[noreturn]]` works better here.
We can't migrate `ABSL_ATTRIBUTE_NORETURN` to use `[[noreturn]]`
because the difference in accepted attribute placement
breaks some code.
PiperOrigin-RevId: 648395324
Change-Id: Icd3e9b837aac25f128e8994de099f1edb3cabccf
