libc: enable sprintf FORTIFY_SOURCE under clang

clang doesn't support __builtin_va_arg_pack(), so we have
to use #define instead.

Change-Id: I2ee75e6267d60cdf997fee6b9b0547bf68f062a1
diff --git a/tests/fortify2_test.cpp b/tests/fortify2_test.cpp
index b6f6661..2f50038 100644
--- a/tests/fortify2_test.cpp
+++ b/tests/fortify2_test.cpp
@@ -46,6 +46,13 @@
               testing::KilledBySignal(SIGABRT), "");
 }
 
+TEST(Fortify2_DeathTest, sprintf2_fortified2) {
+  ::testing::FLAGS_gtest_death_test_style = "threadsafe";
+  foo myfoo;
+  ASSERT_EXIT(sprintf(myfoo.a, "0123456789"),
+              testing::KilledBySignal(SIGABRT), "");
+}
+
 #if __BIONIC__
 // zero sized target with "\0" source (should fail)
 TEST(Fortify2_DeathTest, strcpy_fortified2) {
@@ -229,6 +236,12 @@
   ASSERT_EXIT(sprintf(buf, "%s", source_buf), testing::KilledBySignal(SIGABRT), "");
 }
 
+TEST(Fortify2_DeathTest, sprintf2_fortified) {
+  ::testing::FLAGS_gtest_death_test_style = "threadsafe";
+  char buf[5];
+  ASSERT_EXIT(sprintf(buf, "aaaaa"), testing::KilledBySignal(SIGABRT), "");
+}
+
 TEST(Fortify2_DeathTest, strncat_fortified) {
   ::testing::FLAGS_gtest_death_test_style = "threadsafe";
   char buf[10];