Added a test.

src/test/ui/loops/loop-no-implicit-break.rs

@@ -0,0 +1,5 @@
+fn main() {
+    let x: i8 = loop {
+        10 //~ ERROR mismatched types
+    };
+}

src/test/ui/loops/loop-no-implicit-break.stderr

@@ -0,0 +1,14 @@
+error[E0308]: mismatched types
+  --> $DIR/loop-no-implicit-break.rs:3:9
+   |
+LL |         10
+   |         ^^ expected `()`, found integer
+   |
+help: you might have meant to break the loop with this value
+   |
+LL |         break 10;
+   |         ^^^^^   ^
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0308`.