Don't declare SYS_* constants for unavailable __NR_* constants.

Bug: https://code.google.com/p/android/issues/detail?id=215853
Change-Id: Iaaa3ce888deb8d032208bf636b7badaed6a72d30
diff --git a/tests/sys_syscall_test.cpp b/tests/sys_syscall_test.cpp
index 9c5e350..68a7167 100644
--- a/tests/sys_syscall_test.cpp
+++ b/tests/sys_syscall_test.cpp
@@ -21,3 +21,10 @@
 TEST(unistd, syscall) {
   ASSERT_EQ(getpid(), syscall(SYS_getpid));
 }
+
+// https://code.google.com/p/android/issues/detail?id=215853
+#if defined(__LP64__)
+  #if defined(SYS_mmap2)
+    #error SYS_mmap2 should not be defined for LP64
+  #endif
+#endif