[libclc] fix compiler check with --target=spirv64 and -disable-llvm-passes (#185376)

Fix "unknown target triple" errors when LLVM_TARGETS_TO_BUILD is empty.

Adding -disable-llvm-passes reduces this to a very basic sanity check
of Clang frontend. This allows the test to pass even if SPIR-V backend
is not enabled, as the frontend can still generate IR for the target.

libclc/cmake/modules/CMakeTestCLCCompiler.cmake

@@ -15,8 +15,8 @@ file(MAKE_DIRECTORY "${_test_dir}")
 message(STATUS "Check for working CLC compiler: ${CMAKE_CLC_COMPILER}")
 
 execute_process(
-  COMMAND "${CMAKE_CLC_COMPILER}" -x cl -c -flto
-          -o "${_test_out}" "${_test_file}"
+  COMMAND "${CMAKE_CLC_COMPILER}" --target=spirv64-unknown-unknown -x cl -c -flto
+          -disable-llvm-passes -o "${_test_out}" "${_test_file}"
   RESULT_VARIABLE _clc_result
   ERROR_VARIABLE _clc_error
 )