[AVR] Use the correct address space for non-prototyped function calls

Some function declarations like this:

    void foo();

do not have a type declaration, for that you'd use:

    void foo(void);

Clang internally bitcasts the variadic function declaration to a
function pointer, but doesn't use the correct address space on AVR. This
commit fixes that.

This fix is necessary to let Clang compile compiler-rt for AVR.

Differential Revision: https://reviews.llvm.org/D78125
diff --git a/clang/lib/CodeGen/CGExpr.cpp b/clang/lib/CodeGen/CGExpr.cpp
index eca76f3..85c2d31 100644
--- a/clang/lib/CodeGen/CGExpr.cpp
+++ b/clang/lib/CodeGen/CGExpr.cpp
@@ -5063,7 +5063,8 @@
   // to the function type.
   if (isa<FunctionNoProtoType>(FnType) || Chain) {
     llvm::Type *CalleeTy = getTypes().GetFunctionType(FnInfo);
-    CalleeTy = CalleeTy->getPointerTo();
+    int AS = Callee.getFunctionPointer()->getType()->getPointerAddressSpace();
+    CalleeTy = CalleeTy->getPointerTo(AS);
 
     llvm::Value *CalleePtr = Callee.getFunctionPointer();
     CalleePtr = Builder.CreateBitCast(CalleePtr, CalleeTy, "callee.knr.cast");