This reverts commit 97aa593a8387586095b7eac12974ba2fdd08f4c3 as it
causes problems (PR45453) https://reviews.llvm.org/D77574#1966321.
This additionally adds an explicit reference to FrontendOpenMP to
clang-tidy where ASTMatchers is used.
This is hopefully just a temporary solution. The dependence on
FrontendOpenMP from ASTMatchers should be handled by CMake
implicitly, not us explicitly.