CodeGen: Don't crash when replacing functions

The peculiarities of C99 create scenario where an LLVM IR function
declaration may need to be replaced with a definition baring a different
type because the prototype and definition are not required to agree.

However, we were not properly deferring this when it occurred.

This fixes PR19280.

llvm-svn: 205099

clang/lib/CodeGen/CodeGenModule.cpp

@@ -1177,12 +1177,14 @@ void CodeGenModule::EmitGlobal(GlobalDecl GD) {
       if (!FD->doesDeclarationForceExternallyVisibleDefinition())
         return;
 
-      const FunctionDecl *InlineDefinition = 0;
-      FD->getBody(InlineDefinition);
-
       StringRef MangledName = getMangledName(GD);
-      DeferredDecls.erase(MangledName);
-      EmitGlobalDefinition(InlineDefinition);
+
+      // Compute the function info and LLVM type.
+      const CGFunctionInfo &FI = getTypes().arrangeGlobalDeclaration(GD);
+      llvm::Type *Ty = getTypes().GetFunctionType(FI);
+
+      GetOrCreateLLVMFunction(MangledName, Ty, GD, /*ForVTable=*/false,
+                              /*DontDefer=*/false);
       return;
     }
   } else {