Auto-sync with upstream branch release/2.26/master
    
    Upstream commit: a81c1156c1a9a6161d49b295a09a4e4cff7a88d0
    
    - posix: Fix improper assert in Linux posix_spawn (swbz#22273)
    - posix: Do not use WNOHANG in waitpid call for Linux posix_spawn
    - posix: Fix compat glob code on s390 and alpha
    - posix: Consolidate Linux glob implementation
    - Fix range check in do_tunable_update_val
    - Let signbit use the builtin in C++ mode with gcc < 6.x (swbz#22296)
    - x86-64: Don't set GLRO(dl_platform) to NULL (swbz#22299)
    - x86-64: Use fxsave/xsave/xsavec in _dl_runtime_resolve (swbz#21265)