[Offload] Build libcxx on the GPU libc bot (#157673)

Author: jhuber6

offload/cmake/caches/AMDGPULibcBot.cmake

@@ -17,5 +17,6 @@ set(CLANG_DEFAULT_LINKER "lld" CACHE STRING "")
 set(CLANG_DEFAULT_RTLIB "compiler-rt" STRING "")
 
 set(LLVM_RUNTIME_TARGETS default;amdgcn-amd-amdhsa CACHE STRING "")
-set(RUNTIMES_amdgcn-amd-amdhsa_LLVM_ENABLE_RUNTIMES "compiler-rt;openmp;libc" CACHE STRING "")
+set(RUNTIMES_amdgcn-amd-amdhsa_CACHE_FILES "${CMAKE_SOURCE_DIR}/../libcxx/cmake/caches/AMDGPU.cmake" CACHE STRING "")
+set(RUNTIMES_amdgcn-amd-amdhsa_LLVM_ENABLE_RUNTIMES "compiler-rt;openmp;libc;libcxxabi;libcxx" CACHE STRING "")
 set(RUNTIMES_amdgcn-amd-amdhsa_LIBC_GPU_TEST_JOBS 4 CACHE STRING "")