Hide __signalfd4, used to implement signalfd(3).

Bug: 11156955
Change-Id: I50842279cb5b32ec8bd45193435574e415cd806e
diff --git a/libc/arch-arm/syscalls/signalfd4.S b/libc/arch-arm/syscalls/__signalfd4.S
similarity index 87%
rename from libc/arch-arm/syscalls/signalfd4.S
rename to libc/arch-arm/syscalls/__signalfd4.S
index f8d8a28..712f975 100644
--- a/libc/arch-arm/syscalls/signalfd4.S
+++ b/libc/arch-arm/syscalls/__signalfd4.S
@@ -2,7 +2,7 @@
 
 #include <private/bionic_asm.h>
 
-ENTRY(signalfd4)
+ENTRY(__signalfd4)
     mov     ip, r7
     ldr     r7, =__NR_signalfd4
     swi     #0
@@ -11,4 +11,4 @@
     bxls    lr
     neg     r0, r0
     b       __set_errno
-END(signalfd4)
+END(__signalfd4)