testsuite: Fix PR threads/19422 regression + Guile regression

The PR threads/19422 patchset added a new regression.

Additionally below it there was already a regression if --with-guile (which is
default if Guile is found) was used.

racy case #1:

(xgdb) PASS: gdb.gdb/selftest.exp: Set xgdb_prompt
^M
Thread 1 "xgdb" received signal SIGINT, Interrupt.^M
0x00007ffff583bfdd in poll () from /lib64/libc.so.6^M
(gdb) FAIL: gdb.gdb/selftest.exp: send ^C to child process
signal SIGINT^M
Continuing with signal SIGINT.^M
^C^M
Thread 1 "xgdb" received signal SIGINT, Interrupt.^M
0x00007ffff5779da0 in sigprocmask () from /lib64/libc.so.6^M
(gdb) PASS: gdb.gdb/selftest.exp: send SIGINT signal to child process
backtrace^M
errstring=errstring@entry=0x7e0e6c "", mask=mask@entry=RETURN_MASK_ALL) at exceptions.c:240^M
errstring=errstring@entry=0x7e0e6c "", mask=mask@entry=RETURN_MASK_ALL) at exceptions.c:240^M
(gdb) PASS: gdb.gdb/selftest.exp: backtrace through signal handler

racy case #2:

(xgdb) PASS: gdb.gdb/selftest.exp: Set xgdb_prompt
^M
Thread 1 "xgdb" received signal SIGINT, Interrupt.^M
0x00007ffff583bfdd in poll () from /lib64/libc.so.6^M
(gdb) FAIL: gdb.gdb/selftest.exp: send ^C to child process
signal SIGINT^M
Continuing with signal SIGINT.^M
^C^M
Thread 2 "xgdb" received signal SIGINT, Interrupt.^M
[Switching to Thread 0x7ffff3b7f700 (LWP 13227)]^M
0x00007ffff6b88b10 in pthread_cond_wait@@GLIBC_2.3.2 () from /lib64/libpthread.so.0^M
(gdb) PASS: gdb.gdb/selftest.exp: send SIGINT signal to child process
backtrace^M
(gdb) FAIL: gdb.gdb/selftest.exp: backtrace through signal handler

Pedro Alves:
Not all targets support thread names, and even those that do, not all
use the program name as default thread name -- I think that's only true
for GNU/Linux, actually.  So I think it's best to not expect that, like:
            -re "(Thread .*|Program) received signal SIGINT.*$gdb_prompt $" {

gdb/testsuite/ChangeLog
2016-01-22  Jan Kratochvil  <[email protected]>

	Fix testsuite compatibility with Guile.
	* gdb.gdb/selftest.exp (send ^C to child process): Accept also Thread.
	(thread 1): New test for backtrace through signal handler.

gdb/testsuite/ChangeLog

@@ -1,3 +1,9 @@
+2016-01-22  Jan Kratochvil  <[email protected]>
+
+	Fix testsuite compatibility with Guile.
+	* gdb.gdb/selftest.exp (send ^C to child process): Accept also Thread.
+	(thread 1): New test for backtrace through signal handler.
+
 2016-01-22  Yao Qi  <[email protected]>
 
 	PR testsuite/19491

gdb/testsuite/gdb.gdb/selftest.exp

@@ -436,8 +436,9 @@ proc test_with_self { executable } {
     if ![target_info exists gdb,nointerrupts] {
 	set description "send ^C to child process"
 	send_gdb "\003"
+	# "Thread 1" is displayed iff Guile support is linked in.
 	gdb_expect {
-	    -re "Program received signal SIGINT.*$gdb_prompt $" {
+	    -re "(Thread 1 .*|Program) received signal SIGINT.*$gdb_prompt $" {
 		pass "$description"
 	    }
 	    -re ".*$gdb_prompt $" {
@@ -453,6 +454,10 @@ proc test_with_self { executable } {
     gdb_test "signal SIGINT" \
 	"Continuing with signal SIGINT.*" \
 	"$description"
+
+    # Switch back to the GDB thread if Guile support is linked in.
+    # "signal SIGINT" could also switch the current thread.
+    gdb_test "thread 1" {\[Switching to thread 1 .*\].*}
 
     # get a stack trace
     #