Hide __signalfd4, used to implement signalfd(3).

Bug: 11156955
Change-Id: I50842279cb5b32ec8bd45193435574e415cd806e
diff --git a/libc/SYSCALLS.TXT b/libc/SYSCALLS.TXT
index 83feb65..4a21582 100644
--- a/libc/SYSCALLS.TXT
+++ b/libc/SYSCALLS.TXT
@@ -228,7 +228,7 @@
 int     __rt_sigprocmask:rt_sigprocmask(int, const sigset_t*, sigset_t*, size_t)  all
 int     __rt_sigsuspend:rt_sigsuspend(const sigset_t*, size_t)  all
 int     __rt_sigtimedwait:rt_sigtimedwait(const sigset_t*, struct siginfo_t*, struct timespec_t*, size_t)  all
-int     signalfd4(int, const sigset_t*, size_t, int)  all
+int     __signalfd4:signalfd4(int, const sigset_t*, size_t, int)  all
 
 # sockets
 int           socket(int, int, int)              arm,arm64,mips,mips64,x86_64