Disable ABSL_ATTRIBUTE_TRIVIAL_ABI in open-source builds (#1606)

Since compiler support for this attribute differs, if for example
system libraries compiled with GCC are mixed with libraries compiled
with Clang, types will have different ideas about their ABI.

PiperOrigin-RevId: 600467146

absl/base/attributes.h

@@ -843,15 +843,11 @@
 // See also the upstream documentation:
 // https://clang.llvm.org/docs/AttributeReference.html#trivial-abi
 //
-#if ABSL_HAVE_CPP_ATTRIBUTE(clang::trivial_abi)
-#define ABSL_ATTRIBUTE_TRIVIAL_ABI [[clang::trivial_abi]]
-#define ABSL_HAVE_ATTRIBUTE_TRIVIAL_ABI 1
-#elif ABSL_HAVE_ATTRIBUTE(trivial_abi)
-#define ABSL_ATTRIBUTE_TRIVIAL_ABI __attribute__((trivial_abi))
-#define ABSL_HAVE_ATTRIBUTE_TRIVIAL_ABI 1
-#else
+// b/321691395 - This is currently disabled in open-source builds since
+// compiler support differs. If system libraries compiled with GCC are mixed
+// with libraries compiled with Clang, types will have different ideas about
+// their ABI, leading to hard to debug crashes.
 #define ABSL_ATTRIBUTE_TRIVIAL_ABI
-#endif
 
 // ABSL_ATTRIBUTE_NO_UNIQUE_ADDRESS
 //