[gdb/testsuite] Fix gdb.server/server-kill.exp with -m32

When running test-case gdb.server/server-kill.exp with target board unix/-m32,
I run into:
...
0xf7fd6b20 in _start () from /lib/ld-linux.so.2^M
(gdb) Executing on target: kill -9 13082    (timeout = 300)
builtin_spawn -ignore SIGHUP kill -9 13082^M
bt^M
(gdb) FAIL: gdb.server/server-kill.exp: kill_pid_of=server: test_unwind_syms: bt
...

The test-case expects the backtrace command to trigger remote communication,
which then should result in a "Remote connection closed" or similar.

However, no remote communication is triggered, because we hit the "Check that
this frame is unwindable" case in get_prev_frame_always_1.

We don't hit this problem in the kill_pid_of=inferior case, because there we
run to main before doing the backtrace.

Fix this by doing the same in the kill_pid_of=server case.

Tested on x86_64-linux.

1 files changed, 6 insertions, 4 deletions

diff --git a/gdb/testsuite/gdb.server/server-kill.exp b/gdb/testsuite/gdb.server/server-kill.exp
index 655821c..4125e5b 100644
--- a/gdb/testsuite/gdb.server/server-kill.exp
+++ b/gdb/testsuite/gdb.server/server-kill.exp
@@ -69,11 +69,13 @@ proc prepare {} {
 
     gdbserver_run ""
 
-    if { $::kill_pid_of == "inferior" } {
-	# Continue past server_pid assignment.
-	gdb_breakpoint ${srcfile}:[gdb_get_line_number "i = 0;"]
-	gdb_continue_to_breakpoint "after server_pid assignment"
+    # Continue past server_pid assignment.  We do this for both scenarios,
+    # to avoid doing a backtrace from _start, which may not trigger remote
+    # communication.
+    gdb_breakpoint ${srcfile}:[gdb_get_line_number "i = 0;"]
+    gdb_continue_to_breakpoint "after server_pid assignment"
 
+    if { $::kill_pid_of == "inferior" } {
 	# Get the pid of GDBServer.
 	set test "p server_pid"
 	set server_pid 0