Pass _CL_DISABLE_LONG via API mode too.
The affected devices, basic and pthread, check the result of ./configure,
and set a flag in _cl_device that is then checked when building the clang compilation.

However, with this setup, clang reports:
clang: warning: argument unused during compilation: '-D _CL_DISABLE_LONG'
but compiles the kernels just fine. Removing the _CL_DISABLE_LONG causes the static
assert (sizeof(long)!=8).