Add test accessing the module level int/float consts

Author: faern

src/test/ui/use-module-level-int-consts.rs

@@ -0,0 +1,11 @@
+// run-pass
+
+// Make sure the module level constants are still there and accessible even after
+// the corresponding associated constants have been added, and later stabilized.
+use std::{u16, f32};
+
+fn main() {
+    let _ = u16::MAX;
+    let _ = f32::EPSILON;
+    let _ = std::f64::MANTISSA_DIGITS;
+}