Skip gdb.base/branch-to-self.exp if gdb,nosignals exists

I get a timeout fail in branch-to-self.exp when it is compiled by a
bare-mental target running qemu, which doesn't have signal.

The test should be skipped if gdb,nosignals exists, and that is
what this patch does.

gdb/testsuite:

2016-04-27  Yao Qi  <yao.qi@linaro.org>

	* gdb.base/branch-to-self.exp: Skip it if gdb,nosignals
	exists.

gdb/testsuite/ChangeLog

@@ -1,3 +1,8 @@
+2016-04-27  Yao Qi  <yao.qi@linaro.org>
+
+	* gdb.base/branch-to-self.exp: Skip it if gdb,nosignals
+	exists.
+
 2016-04-26  Bernhard Heckel  <bernhard.heckel@intel.com>
 
 	* vla-type.exp: Print structure from toplevel.

gdb/testsuite/gdb.base/branch-to-self.exp

@@ -15,6 +15,11 @@
 # You should have received a copy of the GNU General Public License
 # along with this program.  If not, see <http://www.gnu.org/licenses/>.
 
+if [target_info exists gdb,nosignals] {
+    verbose "Skipping branch-to-self.exp because of nosignals."
+    continue
+}
+
 standard_testfile
 
 if { [build_executable ${testfile}.exp ${testfile} $srcfile {debug}] == -1 } {