I've sent a whole bunch of patches to the libclc dev list implementing quite a
few builtin CL functions that were missing.  luxrays/slg4 is now able to
compile the CL kernels, but it now gets an LLVM Error at a later point.

[SLG] [PathOCLRenderThread::0] Kernels compilation time: 290ms
*** r600_compute_global_buffer_create
width = 4951104 array_size = 0
* compute_memory_alloc() size_in_dw = 1237776 (4951104 bytes)
  + Adding item 0x5ce9c70 id = 0 size = 1237776 (4951104 bytes)
*** evergreen_create_compute_state
LLVM ERROR: not a number, or does not fit in an unsigned int
* compute_memory_pool_delete()