"Enable precompiled headers" breaks build

[frantisekz]

Since #297 , the build fails with multiple repeating errors:

CMake Error at cl_headers/CMakeLists.txt:36 (add_custom_command):
  Error evaluating generator expression:

    $<TARGET_FILE:clang>

  No target "clang"

(on every call to create_pcm)

I've tested b3b2d7f against LLVM 16 with -DPREFERRED_LLVM_VERSION=16.0.0 (llvm from system, spirv-llvm-translator from system built as a .so).

@haonanya do you have any ideas here?

[frantisekz]

Pinging again, @haonanya , would you have some cycles to take a look please? It seems it's currently impossible to build opencl-clang as standalone library (which is required for distributions).

Thanks!