Use more accurate pointer type

Author: tblah

flang/include/flang/Optimizer/Builder/Runtime/RTBuilder.h

@@ -139,8 +139,9 @@ constexpr TypeBuilderFunc getModel<void *>() {
 template <>
 constexpr TypeBuilderFunc getModel<void (*)(int)>() {
   return [](mlir::MLIRContext *context) -> mlir::Type {
-    return fir::LLVMPointerType::get(context,
-                                     mlir::IntegerType::get(context, 8));
+    return fir::LLVMPointerType::get(
+        context,
+        mlir::FunctionType::get(context, /*inputs=*/{}, /*results*/ {}));
   };
 }
 template <>