Auto-sync with upstream branch master
    
    commit 2ef427168818ce04b03cecb7b739f9db0156e3e4
    
    - Require GCC 5 or later to build glibc (swbz#23993)
    - Only build libm with -fno-math-errno (swbz#24024)
    - sysdeps/ieee754: prevent maybe-uninitialized errors with -O (swbz#19444)
    - Multiple locales: Use the correct 12-hour time formats (swbz#10496)
    - sq_AL: Use the correct date and time formats (swbz#10496, swbz#23724)
    - en_US: define date_fmt (swbz#24046)
    - Remove executable bit from localedata/locales/bi_VU (swbz#23995)
    - malloc: Always call memcpy in _int_realloc (swbz#24027)
    - ARM: fix kernel assisted atomics with GCC 8 (swbz#24034)
    - S390: Unify 31/64bit mem{set,cmp,cpy,pcpy}, bzero with ifunc handling
    - S390: Refactor ifunc handling for several str* and wc* functions
    - posix: Clear close-on-exec for posix_spawn adddup2 (swbz#23640)
    - termios: Define TIOCSER_TEMT with __USE_MISC (swbz#17783)
    - termios: Consolidate Baud Rate Selection definitions (swbz#23783)
    - Y2038: add __{localtime64,gmttime64,ctime64}[_r] functions
    - Y2038: make __difftime compatible with 64-bit time