Auto-sync with upstream branch master
    
    Upstream commit: 4eda036f5b897fa8bc20ddd2099b5a6ed4239dc9
    
    - stdlib: Move tst-system to tests-container
    - support/shell-container.c: Add builtin kill
    - support/shell-container.c: Add builtin exit
    - support/shell-container.c: Return 127 if execve fails
    - Add NEWS entry for CVE-2020-1751 (bug 25423)
    - posix: Fix system error return value [BZ #25715]
    - y2038: fix: Add missing libc_hidden_def attribute for some syscall wrappers
    - Extended Char Intro: Use getwc in example (Bug 25626)
    - stdio: Add tests for printf multibyte convertion leak [BZ#25691]
    - stdio: Remove memory leak from multibyte convertion [BZ#25691]
    - Add NEWS entry for CVE-2020-1752 (bug 25414)
    - math: Remove inline math tests
    - Remove __LIBC_INTERNAL_MATH_INLINES
    - math: Remove mathinline
    - m68k: Remove mathinline.h
    - oc_FR locale: Fix spelling of Thursday (bug 25639)
    - x86: Remove ARCH_CET_LEGACY_BITMAP [BZ #25397]
    - Fix build with GCC 10 when long double = double.
    - nscd/cachedumper.c : fix whitespace
    - Fix nscd/cachedumper.c compile errors
    - manual: Fix inconsistent declaration of wcsrchr [BZ #24655]
    - nscd: add cache dumper