Auto-sync with upstream branch master,
    
    Upstream commit 46ae07324b1cd50fbf8f37a076d6babcfca7c510
    
    - Improve string benchtest timing
    - sysvipc: Add missing bit of semtimedop s390 consolidation
    - wcsmbs: Fix data race in __wcsmbs_clone_conv [swbz #24584]
    - libio: Fix gconv-related memory leak [swbz #24583]
    - libio: Remove codecvt vtable [swbz #24588]
    - support: Expose sbindir as support_sbindir_prefix
    - support: Add missing EOL terminators on timespec
    - support: Correct confusing comment
    - sysvipc: Consolidate semtimedop s390
    - sysvipc: Fix compat msgctl (swbz#24570)
    - Add NT_ARM_PACA_KEYS and NT_ARM_PACG_KEYS from Linux 5.1 to elf.h.
    - Small tcache improvements
    - manual: Document O_DIRECTORY
    - Update kernel-features.h files for Linux 5.1.
    - nss_nis, nss_nisplus: Remove RES_USE_INET6 handling
    - nss_files: Remove RES_USE_INET6 from hosts processing
    - support: Report NULL blobs explicitly in TEST_COMPARE
    - dlfcn: Guard __dlerror_main_freeres with __libc_once_get (once) [swbz# 24476]
    - Add missing Changelog entry