also test div-by-minus-1

Author: RalfJung

tests/compile-fail/unchecked_div1.rs

@@ -0,0 +1,5 @@
+#![feature(core_intrinsics)]
+fn main() {
+    // MIN/-1 cannot be represented
+    unsafe { std::intrinsics::unchecked_div(i16::min_value(), -1); } //~ ERROR Overflow executing `unchecked_div`
+}