[GPGPU] Fix #includes.

Adapt for 05da2fe521 "Sink all InitializePasses.h includes" which
forgot the GPGPU files (presumably because POLLY_ENABLE_GPGPU_CODEGEN
is OFF by default).

polly/lib/CodeGen/ManagedMemoryRewrite.cpp

@@ -23,6 +23,7 @@
 #include "polly/ScopDetection.h"
 #include "llvm/ADT/SmallSet.h"
 #include "llvm/Analysis/CaptureTracking.h"
+#include "llvm/InitializePasses.h"
 #include "llvm/Transforms/Utils/ModuleUtils.h"
 
 using namespace polly;

polly/lib/CodeGen/PPCGCodeGeneration.cpp

@@ -28,6 +28,7 @@
 #include "llvm/IR/LegacyPassManager.h"
 #include "llvm/IR/Verifier.h"
 #include "llvm/IRReader/IRReader.h"
+#include "llvm/InitializePasses.h"
 #include "llvm/Linker/Linker.h"
 #include "llvm/Support/SourceMgr.h"
 #include "llvm/Support/TargetRegistry.h"