Auto-sync with upstream branch master
    
    Upstream commit: f1a844ac6389ea4e111afc019323ca982b5b027d
    
    - CVE-2017-16997: elf: Check for empty tokens before DST expansion (#1526866)
    - Remove sln (#1531546)
    - Remove Sun RPC interfaces (#1531540)
    - Rebuild with newer GCC to fix pthread_exit stack unwinding issue (#1529549)
    - i386: In makecontext, align the stack before calling exit (swbz#22667)
    - x86, armhfp: sync sys/ptrace.h with Linux 4.15 (swbz#22433)
    - elf: check for rpath emptiness before making a copy of it
    - elf: remove redundant is_path argument
    - elf: remove redundant code from is_dst
    - elf: remove redundant code from _dl_dst_substitute
    - scandir: fix wrong assumption about errno (swbz#17804)
    - Deprecate external use of libio.h and _G_config.h