Merge #19111: Limit scope of all global std::once_flag

fa9c67559186f5416c1c0b26c0a1d5e72c234ccb Limit scope of all global std::once_flag (MarcoFalke)

Pull request description:

  `once_flag` is  a helper (as the name might suggest) to execute a callable only once. Thus, the scope of the flag does never need to extend beyond where the callable is called. Typically this is function scope.

  Move all the flags to function scope to
  * simplify code review
  * avoid mistakes where similarly named flags are accidentally exchanged
  * avoid polluting the global scope

ACKs for top commit:
  hebasto:
    ACK fa9c67559186f5416c1c0b26c0a1d5e72c234ccb, tested on Linux Mint 19.3 (x86_64).
  promag:
    Code review ACK fa9c67559186f5416c1c0b26c0a1d5e72c234ccb.

Tree-SHA512: 095a0c11d93d0ddcb82b3c71676090ecc7e3de3d5e7a2a63ab2583093be279242acac43523bbae2060b4dcfa8f92b54256a0e91fbbae78fa92d2d49e9db62e57

0 files changed, 0 insertions, 0 deletions