[clang][OpenMP] 6.0: Add defaultmap implicit-behavior 'storage' (#158336)
First of two patches split from original defaultmap PR:
https://github.com/llvm/llvm-project/pull/157767
Per OpenMP 6.0 specification, section 7.9.9
Argument keywords, page 291, L17
Additional information, page 291, L24-25
24 The value alloc may also be specified as implicit-behavior with
identical meaning to the value 25 storage.
Testing:
Updated 'defaultmap' error message and codegen LIT tests to verify
behavior in OpenMP 6.0.