[clang] [clang][OpenMP] Reduce AST dump tests for 'target' clause (PR #200077)

[Alexey Bataev via cfe-commits]

alexey-bataev wrote:

_messages like tests are not quite relevant, they do not build AST nodes on many cases, check _print and _codegen like tests instead.

https://github.com/llvm/llvm-project/pull/200077