[FastISel] Correctly report prototype on miss

The type of a function is nowadays just an opaque pointer, which is not
helpful when analyzing FastISel misses. Instead print the actual
function type of the function.

Reviewed By: efriedma

Differential Revision: https://reviews.llvm.org/D147716

Author: aengelke

llvm/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp

@@ -1449,7 +1449,7 @@ void SelectionDAGISel::SelectAllBasicBlocks(const Function &Fn) {
                                  Fn.getSubprogram(),
                                  &Fn.getEntryBlock());
       R << "FastISel didn't lower all arguments: "
-        << ore::NV("Prototype", Fn.getType());
+        << ore::NV("Prototype", Fn.getFunctionType());
       reportFastISelFailure(*MF, *ORE, R, EnableFastISelAbort > 1);
 
       // Use SelectionDAG argument lowering