Add a location to verifier error messages.

The verifier reports the 'location' of an error message as a reference
to the entity that has a problem. This uses the 'AnyEntity' type to
refer to instructions/values/ebbs etc.

Also add an err! macro similar to the one used by the parser.

cranelift/src/tools/filetest/runner.rs

@@ -259,7 +259,7 @@ impl Job {
 
         // Should we run the verifier before this test?
         if !context.verified && test.needs_verifier() {
-            try!(verify_function(&func));
+            try!(verify_function(&func).map_err(|e| e.to_string()));
             context.verified = true;
         }
 

cranelift/src/tools/tests/verifier.rs

@@ -41,7 +41,7 @@ fn verifier_tests_from_source(function_source: &str) {
         let result = Verifier::new(&func).run();
         match verifier_results[i] {
             Some(ref re) => {
-                assert_eq!(re.is_match(&result.err().unwrap()), true);
+                assert_eq!(re.is_match(&result.err().unwrap().message), true);
             },
             None => {
                 assert_eq!(result, Ok(()));

cranelift/src/tools/tests/verifier_testdata/bad_layout.cton

@@ -1,4 +1,4 @@
-function test(i32) {    ; Err(terminating)
+function test(i32) {    ; Err(terminator)
     ebb0(v0: i32):
         jump ebb1
         return