Auto-sync with upstream branch master
    
    - Remove glibc-ld-readonly-revert.patch.
    
    Upstream commit e037274c8ec86ca9d491331984b34f30701b23cf:
    
    - stdlib: Fix tst-canon-bz26341 when the glibc build current working
      directory is itself using symlinks.
    - powerpc: Remove backtrace implementation
    - Correct access attribute on memfrob (bug 28475)
    - debug: Add tests for _FORTIFY_SOURCE=3
    - Make sure that the fortified function conditionals are constant
    - Don't add access size hints to fortifiable functions
    - glibcextract.py: Place un-assemblable @@@ in a comment
    - nss: Unnest nested function add_key
    - ld.so: Initialize bootstrap_map.l_ld_readonly [BZ #28340]
    - timex: Use 64-bit fields on 32-bit TIMESIZE=64 systems (BZ #28469)
    - manual: Update _TIME_BITS to clarify it's user defined
    - nptl: Fix tst-cancel7 and tst-cancelx7 pidfile race
    - elf: Fix elf_get_dynamic_info() for bootstrap
    - hurd if_index: Explicitly use AF_INET for if index discovery
    - hurd: Fix intr-msg parameter/stack kludge
    - x86-64: Add test-vector-abi.h/test-vector-abi-sincos.h
    - elf: Fix dynamic-link.h usage on rtld.c