[libclc] [libclc][CMake] Add spir64 target to clang compiler test (PR #185376)

[Matt Arsenault via cfe-commits]

https://github.com/arsenm commented:

This will just move the failure to a build where you didn't build spirv. This should try iterating through the runtime build target triples?

https://github.com/llvm/llvm-project/pull/185376