[clang] [llvm] [OpenMP] Add directive spellings introduced in spec v6.0 (PR #141772)

[Krzysztof Parzyszek via cfe-commits]

kparzysz wrote:

We don't parse them yet, that will require additional changes.  This patch will only affect what names are printed in diagnostic messages.

https://github.com/llvm/llvm-project/pull/141772