Auto-sync with upstream branch master
    
    Upstream commit: 9403b71ae97e3f1a91c796ddcbb4e6f044434734
    
    - x86_64: Remove bzero optimization
    - RISC-V: Use an autoconf template to produce `preconfigure'
    - MIPS: Use an autoconf template to produce `preconfigure'
    - m68k: Use an autoconf template to produce `preconfigure'
    - C-SKY: Use an autoconf template to produce `preconfigure'
    - Remove configure fno_unit_at_a_time
    - stdio: Remove the usage of $(fno-unit-at-a-time) for siglist.c
    - stdio: Remove the usage of $(fno-unit-at-a-time) for errlist.c
    - Add declare_object_symbol_alias for assembly codes (BZ #28128)
    - wcrtomb: Make behavior POSIX compliant