runtime: Fix GDB integration with Python 2

A similar fix was applied in 54568685
but another instance of 'pc' was missed.

Also adds a test for the goroutine gdb command.

It currently uses goroutine 2 for the test, since goroutine 1 has
its stack pointer set to 0 for some reason.

Change-Id: I53ca22be6952f03a862edbdebd9b5c292e0853ae
Reviewed-on: https://go-review.googlesource.com/8729
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

src/runtime/runtime-gdb.py

@@ -446,7 +446,7 @@ class GoroutineCmd(gdb.Command):
 			#python3 / newer versions of gdb
 			pc = int(pc)
 		except gdb.error:
-			pc = int(str(pc), 16)
+			pc = int(str(pc).split(None, 1)[0], 16)
 		save_frame = gdb.selected_frame()
 		gdb.parse_and_eval('$save_pc = $pc')
 		gdb.parse_and_eval('$save_sp = $sp')

src/runtime/runtime-gdb_test.go

@@ -80,6 +80,9 @@ func TestGdbPython(t *testing.T) {
 		"-ex", "echo BEGIN print ptrvar\n",
 		"-ex", "print ptrvar",
 		"-ex", "echo END\n",
+		"-ex", "echo BEGIN goroutine 2 bt\n",
+		"-ex", "goroutine 2 bt",
+		"-ex", "echo END\n",
 		filepath.Join(dir, "a.exe")).CombinedOutput()
 
 	firstLine := bytes.SplitN(got, []byte("\n"), 2)[0]
@@ -112,4 +115,9 @@ func TestGdbPython(t *testing.T) {
 	if bl := blocks["print ptrvar"]; !strVarRe.MatchString(bl) {
 		t.Fatalf("print ptrvar failed: %s", bl)
 	}
+
+	btGoroutineRe := regexp.MustCompile(`^#0\s+runtime.+at`)
+	if bl := blocks["goroutine 2 bt"]; !btGoroutineRe.MatchString(bl) {
+		t.Fatalf("goroutine 2 bt failed: %s", bl)
+	}
 }