1) Fix creation of libpiglitutil_cl.dylib
2) Fix includes of OpenCL.h to finish fixing MacOS build

Previous error message when linking dylib was:

Linking C shared library ../../../../lib/libpiglitutil_cl.dylib
Undefined symbols for architecture x86_64:
  "_piglit_cl_get_test_config", referenced from:
      _piglit_cl_framework_run in piglit-framework-cl.c.o
ld: symbol(s) not found for architecture x86_64

Reviewed-by: Tom Stellard <thomas.stellard@amd.com>