add test checking behavior of matching on floats

tests/ui/match/match-float.rs

@@ -0,0 +1,11 @@
+// run-pass
+// Makes sure we use `==` (not bitwise) semantics for float comparison.
+
+fn main() {
+    const F1: f32 = 0.0;
+    const F2: f32 = -0.0;
+    assert_eq!(F1, F2);
+    assert_ne!(F1.to_bits(), F2.to_bits());
+    assert!(matches!(F1, F2));
+    assert!(matches!(F2, F1));
+}