[PowerPC] Removed `-DLLVM_ENABLE_PROJECTS=flang` to allow flang bot to build flang again

[Conanap]

Summary

Not quite sure why this change works, but it is inline with the behaviour of other buildbots.

This change was prompted due to making -DLLVM_FLANG_NEW_DRIVER=on as default, which required clang to be part of the -DLLVM_ENABLE_PROJECTS. However, adding that causes flang to not be built (even though flang is also part of that flag). all also doesn't seem to build flang, even though flang is part of the definition in CMakeLists.txt.

[gkistanova]

LGTM

buildbot/osuosl/master/config/builders.py

# Flang builders.
     'factory' : UnifiedTreeBuilder.getCmakeWithNinjaBuildFactory(
                     clean=True,
                     depends_on_projects=['llvm', 'mlir', 'clang', 'flang'],
                     checks=['check-flang'],
                     extra_configure_args=[
                         '-DLLVM_TARGETS_TO_BUILD=PowerPC',
                         '-DLLVM_INSTALL_UTILS=ON',
                         '-DCMAKE_CXX_STANDARD=17',
-                        '-DLLVM_ENABLE_PROJECTS=flang',
                         '-DLLVM_LIT_ARGS=-vj 256'
                     ],
                     env={
                         'CC': 'clang',
                         'CXX': 'clang++',
                         'LD': 'lld'
                     })},