4dcc159485
Use the spellings in the generated clause parser. The functions
`get<lang>ClauseKind` and `get<lang>ClauseName` are not yet updated.
The definitions of both clauses and directives now take a list of
"Spelling"s instead of a single string. For example
```
def ACCC_Copyin : Clause<[Spelling<"copyin">,
Spelling<"present_or_copyin">,
Spelling<"pcopyin">]> { ... }
```
A "Spelling" is a versioned string, defaulting to "all versions".
For background information see
https://discourse.llvm.org/t/rfc-alternative-spellings-of-openmp-directives/85507