[opaque pointer types] Pass function types for runtime function calls.

Emit{Nounwind,}RuntimeCall{,OrInvoke} have been modified to take a
FunctionCallee as an argument, and CreateRuntimeFunction has been
modified to return a FunctionCallee. All callers have been updated.

Additionally, CreateBuiltinFunction is removed, as it was redundant
with CreateRuntimeFunction after some previous changes.

Differential Revision: https://reviews.llvm.org/D57668

llvm-svn: 353184
diff --git a/clang/lib/CodeGen/CGDeclCXX.cpp b/clang/lib/CodeGen/CGDeclCXX.cpp
index d527aa9..d85445c 100644
--- a/clang/lib/CodeGen/CGDeclCXX.cpp
+++ b/clang/lib/CodeGen/CGDeclCXX.cpp
@@ -260,10 +260,10 @@
   llvm::FunctionType *atexitTy =
     llvm::FunctionType::get(IntTy, dtorStub->getType(), false);
 
-  llvm::Constant *atexit =
+  llvm::FunctionCallee atexit =
       CGM.CreateRuntimeFunction(atexitTy, "atexit", llvm::AttributeList(),
                                 /*Local=*/true);
-  if (llvm::Function *atexitFn = dyn_cast<llvm::Function>(atexit))
+  if (llvm::Function *atexitFn = dyn_cast<llvm::Function>(atexit.getCallee()))
     atexitFn->setDoesNotThrow();
 
   EmitNounwindRuntimeCall(atexit, dtorStub);