GPGPU: Mark kernel functions as polly.skip

Otherwise, we would try to re-optimize them with Polly-ACC and possibly even
generate kernels that try to offload themselves, which does not work as the
GPURuntime is not available on the accelerator and also does not make any
sense.

llvm-svn: 277589
diff --git a/polly/lib/Analysis/ScopDetection.cpp b/polly/lib/Analysis/ScopDetection.cpp
index 3770ae0..433a72f 100644
--- a/polly/lib/Analysis/ScopDetection.cpp
+++ b/polly/lib/Analysis/ScopDetection.cpp
@@ -1402,7 +1402,7 @@
   return true;
 }
 
-void ScopDetection::markFunctionAsInvalid(Function *F) const {
+void ScopDetection::markFunctionAsInvalid(Function *F) {
   F->addFnAttr(PollySkipFnAttr);
 }