Add test to confirm #3924 fix

gcc/testsuite/ChangeLog:

	* rust/compile/issue-3924.rs: New test.

Signed-off-by: Pierre-Emmanuel Patry <[email protected]>

Author: P-E-P

gcc/testsuite/rust/compile/issue-3924.rs

@@ -0,0 +1,6 @@
+pub fn main() {
+    const S: usize = 23 as i64;
+    // { dg-error {mismatched types, expected .usize. but got .i64.} "" { target *-*-* } .-1 }
+    [0; S];
+    ()
+}