pocl_llvm_api.cc: remove preprocessed sources unless keep-devel-files envvar is set
pocl_llvm_api.cc: remove preprocessed sources unless keep-devel-files envvar is set

pocl/pocl,franz/pocl,rjodin/pocl,franz/pocl,franz/pocl,Oblomov/pocl,Oblomov/pocl,pocl/pocl,pocl/pocl,Oblomov/pocl,jrprice/pocl,jrprice/pocl,franz/pocl,pocl/pocl,jrprice/pocl,Oblomov/pocl,Oblomov/pocl,rjodin/pocl,jrprice/pocl,rjodin/pocl,franz/pocl,rjodin/pocl,pocl/pocl