Add <sys/quota.h>.

It turns out that at least the Nexus 9 kernel is built without CONFIG_QUOTA.
If we decide we're going to mandate quota functionality, I'm happy for us to
be a part of CTS that ensures that happens, but I don't want to be first, so
there's not much to test here other than "will it compile?". The strace
output looks right though.

Bug: http://b/27948821
Bug: http://b/27952303
Change-Id: If667195eee849ed17c8fa9110f6b02907fc8fc04
diff --git a/libc/SYSCALLS.TXT b/libc/SYSCALLS.TXT
index 87f600b..e530293 100644
--- a/libc/SYSCALLS.TXT
+++ b/libc/SYSCALLS.TXT
@@ -322,6 +322,8 @@
 ssize_t process_vm_readv(pid_t, const struct iovec*, unsigned long, const struct iovec*, unsigned long, unsigned long)  all
 ssize_t process_vm_writev(pid_t, const struct iovec*, unsigned long, const struct iovec*, unsigned long, unsigned long)  all
 
+int quotactl(int, const char*, int, char*)  all
+
 int __set_tid_address:set_tid_address(int*)  all
 
 int setfsgid(gid_t)  all