libc: upgrade sprintf to _FORTIFY_SOURCE=2

Upgrade sprintf to fortify_source level 2, to catch
additional security bugs.

Change-Id: Ibc957d65e4cb96152de84b3745a04e00fa22659e
diff --git a/tests/fortify1_test.cpp b/tests/fortify1_test.cpp
index 0cbb8cf..e237193 100644
--- a/tests/fortify1_test.cpp
+++ b/tests/fortify1_test.cpp
@@ -52,3 +52,11 @@
   ASSERT_EXIT(printf("%s", strrchr(buf, 'a')), testing::KilledBySignal(SIGSEGV), "");
 }
 #endif
+
+TEST(Fortify1_DeathTest, sprintf_fortified) {
+  ::testing::FLAGS_gtest_death_test_style = "threadsafe";
+  char buf[10];
+  char source_buf[15];
+  memcpy(source_buf, "12345678901234", 15);
+  ASSERT_EXIT(sprintf(buf, "%s", source_buf), testing::KilledBySignal(SIGSEGV), "");
+}