Auto-sync with upstream branch master
    
    Upstream commit: 32ff397533715988c19cbf3675dcbd727ec13e18
    
    - Fix crash in _IO_wfile_sync (#1710460)
    - nss: Turn __nss_database_lookup into a compatibility symbol
    - support: Add support_install_rootsbindir
    - iconv: Remove public declaration of __gconv_transliterate
    - Linux: Add the tgkill function
    - manual: Adjust twalk_r documentation.
    - elf: Fix tst-pldd for non-default --prefix and/or --bindir (swbz#24544)
    - support: Export bindir path on support_path
    - configure: Make --bindir effective
    - x86: Remove arch-specific low level lock implementation
    - nptl: Assume LLL_LOCK_INITIALIZER is 0
    - nptl: Small optimization for lowlevellock
    - Add single-thread.h header
    - locale: Update to Unicode 12.1.0 (swbz#24535)
    - malloc: Fix tcache count maximum (swbz#24531)
    - sem_close: Use __twalk_r
    - support: Fix timespec printf
    - nptl/tst-abstime: Use libsupport
    - nptl: Convert some rwlock tests to use libsupport
    - nptl: Use recent additions to libsupport in tst-sem5
    - nptl: Convert tst-cond11.c to use libsupport
    - support: Add timespec.h
    - Move nptl/tst-eintr1 to xtests (swbz#24537)
    - powerpc: trunc/truncf refactor
    - powerpc: round/roundf refactor
    - powerpc: floor/floorf refactor
    - support: Add xclock_gettime
    - malloc/tst-mallocfork2: Use process-shared barriers
    - Update syscall-names.list for Linux 5.1
    - Use GCC 9 in build-many-glibcs.py
    - aarch64: thunderx2 memmove performance improvements
    - misc/tst-tsearch: Additional explicit error checking
    - elf: Fix elf/tst-pldd with --enable-hardcoded-path-in-tests (swbz#24506)
    - misc: Add twalk_r function