[PATCH v2 2/2] [gdb/testsuite] Fix timeout in gdb.threads/vfork-multi-inferior.exp

With test-case gdb.threads/vfork-multi-inferior.exp I get either:
...
(gdb) run &
Starting program: vfork-multi-inferior-sleep
(gdb) PASS: $exp: method=non-stop: run inferior 2
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib64/libthread_db.so.1".
inferior 1
[Switching to inferior 1 [<null>] (<noexec>)]
(gdb) PASS: $exp: method=non-stop: inferior 1
...
or:
...
(gdb) run &
Starting program: vfork-multi-inferior-sleep
(gdb) PASS: $exp: method=non-stop: run inferior 2
inferior 1^M
[Switching to inferior 1 [<null>] (<noexec>)]^M
(gdb) PASS: $exp: method=non-stop: inferior 1
[Thread debugging using libthread_db enabled]^M
Using host libthread_db library "/lib64/libthread_db.so.1".^M
...

With a 16.3-based package on aarch64-linux, I ran into:
...
(gdb) run &
Starting program: vfork-multi-inferior-sleep
(gdb) PASS: $exp: method=non-stop: run inferior 2
inferior 1
[Switching to inferior 1 [<null>] (<noexec>)]
(gdb) [Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib64/libthread_db.so.1".
FAIL: $exp: method=non-stop: inferior 1
(timeout)
...

Unfortunately I have not been able to reproduce this.

Fix this using -no-prompt-anchor.

See also commit 5f69c00a6e0 ("[gdb/testsuite] Fix timeout in
gdb.base/async-shell.exp").

Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=34427
---
 gdb/testsuite/gdb.threads/vfork-multi-inferior.exp | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/gdb/testsuite/gdb.threads/vfork-multi-inferior.exp b/gdb/testsuite/gdb.threads/vfork-multi-inferior.exp
index e258ec719e9..f6c90bf0655 100644
--- a/gdb/testsuite/gdb.threads/vfork-multi-inferior.exp
+++ b/gdb/testsuite/gdb.threads/vfork-multi-inferior.exp
@@ -86,7 +86,7 @@ proc do_test {method} {
     }
 
     # Start the first inferior.
-    gdb_test "inferior 1" "Switching to inferior 1 .*"
+    gdb_test -no-prompt-anchor "inferior 1" "Switching to inferior 1 .*"
     gdb_file_cmd ${::binfile}
     gdb_test "break should_break_here" "Breakpoint $::decimal at .*"
     gdb_test "start" "Thread 1.1 .* hit Temporary breakpoint.*" \
-- 
2.51.0