Use pthread_kill() in raise()

raise() should use pthread_kill() in a pthreads environment.
For bionic this means it should always be used.

Change-Id: Ic679272b664d2b8a7068b628fb83a9f7395c441f

tests/signal_test.cpp

@@ -95,3 +95,9 @@ TEST(signal, sigemptyset_invalid) {
 TEST(signal, sigfillset_invalid) {
   TestSigSet1(sigfillset);
 }
+
+TEST(signal, raise_invalid) {
+  errno = 0;
+  ASSERT_EQ(-1, raise(-1));
+  ASSERT_EQ(EINVAL, errno);
+}