valgrind can't find syscall because we didn't put it in <unistd.h>.

Change-Id: I1e47291d4476bd2816138a8cf58f29d4986d39e3
diff --git a/libc/bionic/ndk_cruft.cpp b/libc/bionic/ndk_cruft.cpp
index 28d6355..77412ac 100644
--- a/libc/bionic/ndk_cruft.cpp
+++ b/libc/bionic/ndk_cruft.cpp
@@ -31,6 +31,7 @@
 
 #include <ctype.h>
 #include <dirent.h>
+#include <errno.h>
 #include <inttypes.h>
 #include <pthread.h>
 #include <signal.h>