In "get<lang>DirectiveName(Kind, Version)", return the spelling that
corresponds to Version, and in "get<lang>DirectiveKindAndVersions(Name)"
return the pair {Kind, VersionRange}, where VersionRange contains the
minimum and the maximum versions that allow "Name" as a spelling. This
applies to clauses as well. In general it applies to classes that have
spellings (defined via TableGen class "Spelling").
Given a Kind and a Version, getting the corresponding spelling requires
a runtime search (which can fail in a general case). To avoid generating
the search function inline, a small additional component of
llvm/Frontent was added: LLVMFrontendDirective. The corresponding header
file also defines C++ classes "Spelling" and "VersionRange", which are
used in TableGen/DirectiveEmitter as well.
For background information see
https://discourse.llvm.org/t/rfc-alternative-spellings-of-openmp-directives/85507
7b2aa02a33