Auto-sync with upstream branch master
    
    Upstream commit: 1a85970f41ea1e5abe6da2298a5e8fedcea26b70
    
    - powerpc: Relocate stinfo->main
    - powerpc64: Set up thread register for _dl_relocate_static_pie
    - powerpc64: Use medium model toc accesses throughout
    - linux: Constify rfv variable in dl_vdso_vsym
    - string: Replace outdated comments in strlen().
    - S390: Fix elf/tst-audit25[ab]
    - sparc64: Remove fcopysign{f} implementation
    - alpha: Remove fcopysign{f} implementation
    - math: Use builtin for ldbl-96 copysign
    - ia64: Remove fcopysign{f} implementation
    - x86: Remove fcopysign{f} implementation
    - powerpc: Remove fcopysign{f} implementation
    - Add rif_MA locale [BZ #27781]
    - tests/string: Drop simple/stupid/builtin tests
    - test-memcpy: Actually reverse source and destination
    - benchtests: Only build libmvec benchmarks iff $(build-mathvec) is set