kernel.cl: imported from pocl 5913d434a722451819077e8d00f29ac470153a24

The files are pocl/include/pocl_features.h, pocl_types.h, _kernel.h,
and _kernel_c.h concatenated.
Revert "kernel.cl: imported from pocl 5913d434a722451819077e8d00f29ac470153a24"

This reverts commit 50932deffbb45f20bfd688338a2c901d0e0f0c7f.
kernel.cl: Removed some types introduced by the new clang