Fix const_fn_mir

Author: saethlin

Diff for: tests/run-make/const_fn_mir/dump.mir

@@ -24,16 +24,3 @@ fn foo() -> i32 {
         return;
     }
 }
-
-fn main() -> () {
-    let mut _0: ();
-    let _1: i32;
-
-    bb0: {
-        _1 = foo() -> [return: bb1, unwind continue];
-    }
-
-    bb1: {
-        return;
-    }
-}

Diff for: tests/run-make/const_fn_mir/lib.rs

@@ -0,0 +1,8 @@
+// emit-mir
+//@ check-pass
+
+#![crate_type = "lib"]
+
+pub const fn foo() -> i32 {
+    5 + 6
+}

Diff for: tests/run-make/const_fn_mir/main.rs

@@ -1,10 +1,9 @@
-// The `needs-unwind -Cpanic=abort` gives a different MIR output.
-
-//@ needs-unwind
+//! This test is supposed to check that --emit=mir emits both optimized_mir and mir_for_ctfe for a
+//! const fn.
 
 use run_make_support::{diff, rustc};
 
 fn main() {
-    rustc().input("main.rs").emit("mir").output("dump-actual.mir").run();
+    rustc().input("lib.rs").emit("mir").output("dump-actual.mir").run();
     diff().expected_file("dump.mir").actual_file("dump-actual.mir").run();
 }