[OpenMP][libomp][CMake] use uppercase_CMAKE_BUILD_TYPE

Have standalone builds define uppercase_CMAKE_BUILD_TYPE and use it.
llvm/CMakeLists.txt defines uppercase_CMAKE_BUILD_TYPE for regular LLVM
builds with OpenMP enabled.

Differential Revision: https://reviews.llvm.org/D112951

GitOrigin-RevId: 48b67dca2cccb4898819797240677f490edcf026
1 file changed