slightly update pocl_llvm_build_program
slightly update pocl_llvm_build_program

* change preprocessed output temp file extension
  to distinguish it from temp source files
* always remove it (we have the sources)
* remove temporary sources in 1 place (no need
  to keep them arount for EmitLLVM)

franz/pocl,Oblomov/pocl,pocl/pocl,Oblomov/pocl,pocl/pocl,franz/pocl,franz/pocl,pocl/pocl,pocl/pocl,pocl/pocl,franz/pocl,Oblomov/pocl,Oblomov/pocl,Oblomov/pocl,franz/pocl