Add regression test for const fn in trait

Const fn declaration in trait declarations shall emit an error. This new
test highlight this behavior.

gcc/testsuite/ChangeLog:

	* rust/compile/const_trait_fn.rs: New test.

Signed-off-by: Pierre-Emmanuel Patry <pierre-emmanuel.patry@embecosm.com>

diff --git a/gcc/testsuite/rust/compile/const_trait_fn.rs b/gcc/testsuite/rust/compile/const_trait_fn.rs
new file mode 100644 (file)
index 0000000..cff2f5f
--- /dev/null
+++ b/gcc/testsuite/rust/compile/const_trait_fn.rs
@@ -0,0 +1,4 @@
+trait Osterkz {
+    const fn x();
+    // { dg-error "functions in traits cannot be declared const .E0379." "" { target *-*-* } .-1 }
+}