[gdb/testsuite] Fix gdb.threads/killed-outside.exp with -m32

When running test-case gdb.threads/killed-outside.exp with target board
unix/-m32, we run into:
...
(gdb) PASS: gdb.threads/killed-outside.exp: get pid of inferior
Executing on target: kill -9 10969    (timeout = 300)
spawn -ignore SIGHUP kill -9 10969^M
continue^M
Continuing.^M
[Thread 0xf7cb4b40 (LWP 10973) exited]^M
^M
Program terminated with signal SIGKILL, Killed.^M
The program no longer exists.^M
(gdb) FAIL: gdb.threads/killed-outside.exp: prompt after first continue
...

Fix this by allowing this output.

Tested on x86_64-linux.

gdb/testsuite/ChangeLog:

2021-01-26  Tom de Vries  <tdevries@suse.de>

	* gdb.threads/killed-outside.exp: Allow regular output.

1 files changed, 3 insertions, 0 deletions

diff --git a/gdb/testsuite/gdb.threads/killed-outside.exp b/gdb/testsuite/gdb.threads/killed-outside.exp
index 303328d..7050a4b 100644
--- a/gdb/testsuite/gdb.threads/killed-outside.exp
+++ b/gdb/testsuite/gdb.threads/killed-outside.exp
@@ -54,4 +54,7 @@ gdb_test_multiple "continue" "prompt after first continue" {
 	    }
 	}
     }
+    -re -wrap ".*$killed_msg.*$no_longer_exists_msg" {
+	pass $gdb_test_name
+    }
 }