introduce PrettyPrintMirOptions for cosmetic MIR dump options

initially starting with `-Z mir-include-spans` because we want them in
the NLL mir dump pass

src/base.rs

@@ -44,8 +44,9 @@ pub(crate) fn codegen_fn<'tcx>(
     let _mir_guard = crate::PrintOnPanic(|| {
         let mut buf = Vec::new();
         with_no_trimmed_paths!({
-            rustc_middle::mir::pretty::write_mir_fn(tcx, mir, &mut |_, _| Ok(()), &mut buf)
-                .unwrap();
+            use rustc_middle::mir::pretty;
+            let options = pretty::PrettyPrintMirOptions::from_cli(tcx);
+            pretty::write_mir_fn(tcx, mir, &mut |_, _| Ok(()), &mut buf, options).unwrap();
         });
         String::from_utf8_lossy(&buf).into_owned()
     });