[OpenMP] Fix layering problem with FrontendOpenMP

[jdoerfert]

Summary

ASTMatchers is used in various places and it now exposes the
LLVMFrontendOpenMP library to its users without them needing to depend
on it explicitly.

[lebedev.ri]

LG

[sylvestre.ledru]

@lebedev.ri @jdoerfert Looks like it might have caused:
https://bugs.llvm.org/show_bug.cgi?id=45453

[aheejin]

Could you revert this patch? This is causing an error like this whenever I run clang binary:

: CommandLine Error: Option 'openmp-ir-builder-optimistic-attributes' registered more than once!
LLVM ERROR: inconsistency in registered CommandLine options

This happens when clang is built with -DLLVM_LINK_LLVM_DYLIB=ON -DLLVM_BUILD_LLVM_DYLIB=ON.

[jdoerfert]

In D77574#1967141, @aheejin wrote:

Could you revert this patch? This is causing an error like this whenever I run clang binary:

: CommandLine Error: Option 'openmp-ir-builder-optimistic-attributes' registered more than once!
LLVM ERROR: inconsistency in registered CommandLine options

This happens when clang is built with -DLLVM_LINK_LLVM_DYLIB=ON -DLLVM_BUILD_LLVM_DYLIB=ON.

I'll revert it. Is there a buildbot with this configuration? Do you happen to have insights on how to resolve the issue?

[aheejin]

Thanks. Not sure if there's a buildbot that uses -DLLVM_LINK_LLVM_DYLIB=ON -DLLVM_BUILD_LLVM_DYLIB=ON, but I think you can build with it yourself to reproduce it. About how to resolve the issue, I have no idea, sorry.