check_include_file not respecting CMAKE_PREFIX_PATH

$ file /home/andy/misc/bootstrap/out/native/include/zlib.h
/home/andy/misc/bootstrap/out/native/include/zlib.h: C source, ASCII text

$ cmake /home/andy/misc/bootstrap/llvm-6.0.0.src -DCMAKE_PREFIX_PATH=/home/andy/misc/bootstrap/out/native -DCMAKE_INSTALL_PREFIX=/home/andy/misc/bootstrap/out/native -DCMAKE_BUILD_TYPE=Release -DLLVM_EXPERIMENTAL_TARGETS_TO_BUILD=WebAssembly; \

– Looking for zlib.h - not found

I propose to use find_path and find_library instead of check_include_file. Shall I submit a patch?