Move Rust union tests to new file

I wanted to run the gdb.rust tests against older versions of the Rust
compiler, to ensure that changes I am making don't break debugging
when using older compilers.

However, this did not work because simple.rs now uses unchecked
unions, which were only added in Rust 1.19.

This patch splits the union code into its own file, so that simple.exp
can continue to work.  I tested this with selected rust versions back
to 1.12.

gdb/testsuite/ChangeLog
2020-04-01  Tom Tromey  <tromey@adacore.com>

	* gdb.rust/union.rs: New file.
	* gdb.rust/union.exp: New file.
	* gdb.rust/simple.rs (Union, Union2): Move to union.rs.
	(main): Update.
	* gdb.rust/simple.exp: Move union tests to union.exp.

1 files changed, 35 insertions, 0 deletions

diff --git a/gdb/testsuite/gdb.rust/union.rs b/gdb/testsuite/gdb.rust/union.rs
new file mode 100644
index 0000000..ef30696
--- /dev/null
+++ b/gdb/testsuite/gdb.rust/union.rs
@@ -0,0 +1,35 @@
+// Copyright (C) 2020 Free Software Foundation, Inc.
+
+// This program is free software; you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation; either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+#![allow(dead_code)]
+#![allow(unused_variables)]
+#![allow(unused_assignments)]
+
+
+union Union {
+    f1: i8,
+    f2: u8,
+}
+
+pub union Union2 {
+    pub name: [u8; 1],
+}
+
+fn main() {
+    let u = Union { f2: 255 };
+    let u2 = Union2 { name: [1] };
+
+    println!("Hi");        // set breakpoint here
+}