[clang] [libclc] [clang] Add the ability to link libclc OpenCL libraries (PR #146503)

[Wenju He via cfe-commits]

================
@@ -92,10 +95,14 @@ else()
     get_host_tool_path( llvm-link LLVM_LINK llvm-link_exe llvm-link_target )
     get_host_tool_path( opt OPT opt_exe opt_target )
   endif()
-endif()
 
-# Setup the paths where libclc runtimes should be stored.
-set( LIBCLC_OUTPUT_LIBRARY_DIR ${CMAKE_CURRENT_BINARY_DIR} )
+  # Setup the paths where libclc runtimes should be stored. By default, in an
+  # in-tree build we place the libraries in clang's resource driectory.
+  get_clang_resource_dir( LIBCLC_OUTPUT_DIR PREFIX ${LLVM_LIBRARY_OUTPUT_INTDIR}/.. )
+
+  # Note we do not adhere to LLVM_ENABLE_PER_TARGET_RUNTIME_DIR.
+  set( LIBCLC_OUTPUT_LIBRARY_DIR ${LIBCLC_OUTPUT_DIR}/lib/libclc )
----------------
wenju-he wrote:

When configuring on windows using cmake msvc generator
```
cmake -G "Visual Studio 17 2022" -A x64 -Thost=x64 -DLLVM_ENABLE_PROJECTS="llvm;clang;clang-tools-extra;libclc" -DLLVM_INCLUDE_TESTS=OFF -DLLVM_BUILD_TESTS=OFF -DLLVM_ENABLE_ASSERTIONS=ON -DLLVM_TARGETS_TO_BUILD="X86;AMDGPU" -DCMAKE_INSTALL_PREFIX=install -DCMAKE_BUILD_TYPE=Release -DLIBCLC_TARGETS_TO_BUILD="amdgcn--amdhsa" ../llvm
```
install command in tools\libclc\cmake_install.cmake is not correctly configured as there is a unresolved `$(Configuration)`:
```
if(CMAKE_INSTALL_COMPONENT STREQUAL "Unspecified" OR NOT CMAKE_INSTALL_COMPONENT)
  file(INSTALL DESTINATION "${CMAKE_INSTALL_PREFIX}/share/clc" TYPE FILE FILES "D:/wenjuhe/llvm-project/build/$(Configuration)/lib/../lib/clang/22/lib/libclc/amdgcn--amdhsa.bc")
endif()
```
It causes install error in our downstream project and the error is reproducible in llvm-project:
```
  CMake Error at tools/libclc/cmake_install.cmake:45 (file):
    file INSTALL cannot find
    "D:/wenjuhe/llvm-project/build/$(Configuration)/lib/../lib/clang/22/lib/libclc/amdgcn--amdhsa.bc":
    File exists.
```
@frasercrmck do you have suggestion about why `$(Configuration)` is unresolved?
cmake jinja generator doesn't seem to have the issue because I can build llvm-project and install with ninja.

If I enable libclc in LLVM_ENABLE_RUNTIMES, there is another build error:
```
cmake -G "Visual Studio 17 2022" -A x64 -Thost=x64 -DLLVM_ENABLE_PROJECTS="llvm;clang;clang-tools-extra" -DLLVM_ENABLE_RUNTIMES=libclc -DLLVM_INCLUDE_TESTS=OFF -DLLVM_BUILD_TESTS=OFF -DLLVM_ENABLE_ASSERTIONS=ON -DLLVM_TARGETS_TO_BUILD="X86;AMDGPU" -DCMAKE_INSTALL_PREFIX=install -DCMAKE_BUILD_TYPE=Release -DLIBCLC_TARGETS_TO_BUILD="amdgcn--amdhsa" ../llvm
```
```
Unknown CMake command "get_clang_resource_dir".
```

https://github.com/llvm/llvm-project/pull/146503