The known unsupported OpenCL (both 1.x and 2.x) features are listed here as encountered.
cl_khr_f16: half precision float literals
Compiling “3434.0h” fails with: error: invalid suffix ‘h’ on floating constant
Tested with Clang 3.4 on 2014-07-10.
The list of unimplemented host-side API functions can be seen as the NULLs in the ICD dispatch struct in https://github.com/pocl/pocl/blob/master/lib/CL/clGetPlatformIDs.c