[SYCL] Use a copy to avoid invalidated access (#2495)

This fixes a bug introduced in PR #2430 where the iterator
might get invalidated between accesses.

Signed-off-by: Premanand M Rao <premanand.m.rao@intel.com>

Author: premanandrao

clang/lib/CodeGen/CodeGenModule.cpp

@@ -2273,12 +2273,13 @@ void CodeGenModule::EmitDeferred() {
         auto DDI = DeferredDecls.find(AliaseeName);
         // Emit what is aliased first.
         if (DDI != DeferredDecls.end()) {
-          llvm::GlobalValue *AliaseeGV = dyn_cast<llvm::GlobalValue>(
-              GetAddrOfGlobal(DDI->second, ForDefinition));
+          GlobalDecl GD = DDI->second;
+          llvm::GlobalValue *AliaseeGV =
+              dyn_cast<llvm::GlobalValue>(GetAddrOfGlobal(GD, ForDefinition));
           if (!AliaseeGV)
-            AliaseeGV = GetGlobalValue(getMangledName(DDI->second));
+            AliaseeGV = GetGlobalValue(getMangledName(GD));
           assert(AliaseeGV);
-          EmitGlobalDefinition(DDI->second, AliaseeGV);
+          EmitGlobalDefinition(GD, AliaseeGV);
           // Remove the entry just added to the DeferredDeclsToEmit
           // since we have emitted it.
           DeferredDeclsToEmit.pop_back();