Hide __signalfd4, used to implement signalfd(3).

Bug: 11156955
Change-Id: I50842279cb5b32ec8bd45193435574e415cd806e
diff --git a/libc/arch-x86/syscalls/signalfd4.S b/libc/arch-x86/syscalls/__signalfd4.S
similarity index 94%
rename from libc/arch-x86/syscalls/signalfd4.S
rename to libc/arch-x86/syscalls/__signalfd4.S
index 1fe6c68..7cbe474 100644
--- a/libc/arch-x86/syscalls/signalfd4.S
+++ b/libc/arch-x86/syscalls/__signalfd4.S
@@ -2,7 +2,7 @@
 
 #include <private/bionic_asm.h>
 
-ENTRY(signalfd4)
+ENTRY(__signalfd4)
     pushl   %ebx
     pushl   %ecx
     pushl   %edx
@@ -31,4 +31,4 @@
     popl    %ecx
     popl    %ebx
     ret
-END(signalfd4)
+END(__signalfd4)