[SYCL] Rework MarkDevice and children (#3475)

We identified during a previous review that collectKernelAttributes and
the MarkDeviceFunction object are in a situation that is very difficult
to maintain, so this attempts to fix that by making the ownership model
clear.

Author: Erich Keane

clang/include/clang/Sema/Sema.h

@@ -13190,7 +13190,7 @@ class Sema final {
   void checkSYCLDeviceVarDecl(VarDecl *Var);
   void copySYCLKernelAttrs(const CXXRecordDecl *KernelObj);
   void ConstructOpenCLKernel(FunctionDecl *KernelCallerFunc, MangleContext &MC);
-  void MarkDevice();
+  void MarkDevices();
 
   /// Emit a diagnostic about the given attribute having a deprecated name, and
   /// also emit a fixit hint to generate the new attribute name.

clang/lib/Sema/Sema.cpp

@@ -1039,7 +1039,7 @@ void Sema::ActOnEndOfTranslationUnitFragment(TUFragmentKind Kind) {
       SyclIntHeader->emit(getLangOpts().SYCLIntHeader);
     if (SyclIntFooter != nullptr)
       SyclIntFooter->emit(getLangOpts().SYCLIntFooter);
-    MarkDevice();
+    MarkDevices();
   }
 
   emitDeferredDiags();