Backport cf93a3dd512e4912181f05790992c760378c8893 (remove use of internal glibc macros in libc++) to release/16.x #60517
Description
Commit cf93a3dd512e4912181f05790992c760378c8893 removes use of internal glibc macros (__GLIBC_USE, __GLIBC_USE(ISOC2X)) that were added via commit 7e7013c5d4b1b3996c8dba668c5a94bb33b2999b during LLVM 16 development. These macros have no stability commitments across glibc releases and are not intended to be used outside of glibc source files. Use of these macros therefore creates the potential for inconsistent behavior across future glibc releases.
This issue tracks backporting the commit that removes use of these internal macros so that libc++ in LLVM 16 is not dependent on them.
/cherry-pick cf93a3d