Revert "Add preliminary implementation for GPGPU code generation."

I did not take into account, that this patch fails to compile without the
llvm.codegen patch applied. This breaks buildbots.

I revert this until we found a solution to commit this without buildbots
complaining.

This reverts commit cb43ab80e94434e780a66be3b9a6ad466822fe33.

llvm-svn: 160165