[LibC++][PowerPC] Enable libcxx testing on clang-ppc64le-rhel (#62)

This patch enables the build and test of the libcxx and libcxxabi
runtimes on the clang-ppc64le-rhel buildbot. The compiler toolchain
is updated to use gcc-toolset-12 in order to resolve some libcxx lit
test case failures, we no longer specify the `LLVM_BINUTILS_INCDIR`
since the gold plugin is not being build and ccache is turned on to
improve build times.

Author: kamaub

buildbot/osuosl/master/config/builders.py

@@ -670,17 +670,18 @@
     'builddir': "clang-ppc64le-rhel",
     'factory' : TestSuiteBuilder.getTestSuiteBuildFactory(
                     depends_on_projects=["llvm", "clang", "clang-tools-extra",
-                                         "lld", "compiler-rt"],
-                    checks=['check-all', 'check-runtimes'],
+                                         "lld", "libcxx", "libcxxabi",
+                                         "compiler-rt"],
+                    checks=['check-runtimes', 'check-all'],
                     extra_configure_args=[
                         "-DLLVM_ENABLE_ASSERTIONS=On",
                         "-DCMAKE_C_COMPILER=clang",
                         "-DCMAKE_CXX_COMPILER=clang++",
                         "-DCLANG_DEFAULT_LINKER=lld",
                         "-DLLVM_TOOL_GOLD_BUILD=0",
-                        "-DCMAKE_C_COMPILER_EXTERNAL_TOOLCHAIN:PATH=/usr",
-                        "-DCMAKE_CXX_COMPILER_EXTERNAL_TOOLCHAIN:PATH=/usr",
-                        "-DLLVM_BINUTILS_INCDIR=/usr/include",
+                        "-DCMAKE_C_COMPILER_EXTERNAL_TOOLCHAIN:PATH=/opt/rh/gcc-toolset-12/root/usr",
+                        "-DCMAKE_CXX_COMPILER_EXTERNAL_TOOLCHAIN:PATH=/opt/rh/gcc-toolset-12/root/usr",
+                        "-DLLVM_CCACHE_BUILD=ON",
                         "-DBUILD_SHARED_LIBS=ON", "-DLLVM_ENABLE_WERROR=ON",
                         "-DCMAKE_BUILD_TYPE=Release",
                         "-DLLVM_LIT_ARGS=-vj 20"])},