Auto-sync with upstream branch master
    
    Upstream commit: 7a5db2e82fbb6c3a6e3fdae02b7166c5d0e8c7a8
    
    - elf: Clean up GLIBC_PRIVATE exports of internal libdl symbols
    - nptl: Reduce the GLIBC_PRIVATE ABI
    - nptl: Remove GLIBC_2.34 versions of __pthread_mutex_lock,
      __pthread_mutex_unlock
    - nptl: Use internal low-level lock type for !IS_IN (libc)
    - glibc.malloc.check: Fix nit in documentation
    - Exclude tst-realloc from tests-mcheck
    - linux: Fix setsockopt fallback
    - linux: Use the expected size for SO_TIMESTAMP{NS} convertion
    - linux: Consolidate Linux setsockopt implementation
    - linux: Consolidate Linux getsockopt implementation
    - manual: fix description for preadv()