gdb/testsuite/gdb.threads: Ensure TLS tests link against pthreads.

On Ubuntu by default the compiler passes --as-needed to ld which
means no DT_NEEDED entry is added for libpthread when building
the TLS tests. This causes the test to fail as libpthread is
required to look up TLS variables. Add calls to pthread_testcancel
to make sure libpthread gets linked.

gdb/testsuite/ChangeLog:

2013-07-18  Will Newton  <will.newton@linaro.org>

	* gdb.threads/tls-nodebug.c: Call pthread_testcancel
	to ensure the test is linked against pthreads.
	* gdb.threads/tls-var-main.c: Likewise.
	* gdb.threads/tls-shared.c: Likewise.

gdb/testsuite/ChangeLog

@@ -1,3 +1,10 @@
+2013-07-18  Will Newton  <will.newton@linaro.org>
+
+	* gdb.threads/tls-nodebug.c: Call pthread_testcancel
+	to ensure the test is linked against pthreads.
+	* gdb.threads/tls-var-main.c: Likewise.
+	* gdb.threads/tls-shared.c: Likewise.
+
 2013-07-18  Yao Qi  <yao@codesourcery.com>
 
 	* lib/future.exp (gdb_default_target_compile): Use tail name

gdb/testsuite/gdb.threads/tls-nodebug.c

@@ -6,5 +6,7 @@ __thread int thread_local = 42;
 
 int main(void)
 {
+  /* Ensure we link against pthreads even with --as-needed.  */
+  pthread_testcancel();
   return 0;
 }

gdb/testsuite/gdb.threads/tls-shared.c

@@ -1,6 +1,11 @@
+
+#include <pthread.h>
+
 __thread int i_tls = 1;
 int foo ()
 {
+  /* Ensure we link against pthreads even with --as-needed.  */
+  pthread_testcancel();
   return i_tls;
 }
 

gdb/testsuite/gdb.threads/tls-var-main.c

@@ -15,8 +15,12 @@
    You should have received a copy of the GNU General Public License
    along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
 
+#include <pthread.h>
+
 int
 main (void)
 {
+  /* Ensure we link against pthreads even with --as-needed.  */
+  pthread_testcancel();
   return 0;
 }