[libcxx] Add cache file for the GPU build (#99348)

Summary:
This patch adds a CMake cache config file for the GPU build. This cache
will set the default required options when used from the LLVM runtime
interface or directly. These options pretty much disable everything the
GPU can't handle.

With this and the following patches: #99259, #99243, #99287, and #99333,
we will be able to build `libc++` targeting the GPU with an invocation
like this.

```
$ cmake ../llvm
-DRUNTIMES_nvptx64-nvidia-cuda_CACHE_FILES=${LLVM_SRC}/../libcxx/cmake/caches/NVPTX.cmake \
-DRUNTIMES_amdgcn-amd-amdhsa_CACHE_FILES=${LLVM_SRC}/../libcxx/cmake/caches/AMDGPU.cmake \                            
-DRUNTIMES_nvptx64-nvidia-cuda_LLVM_ENABLE_RUNTIMES=compiler-rt;libc;libcxx \
-DRUNTIMES_amdgcn-amd-amdhsa_LLVM_ENABLE_RUNTIMES=compiler-rt;libc;libcxx   \
-DLLVM_RUNTIME_TARGETS=amdgcn-amd-amdhsa;nvptx64-nvidia-cuda                \
```

This will then install the libraries and headers into the appropriate
locations for use with `clang`.

0 files changed, 0 insertions, 0 deletions