Make __set_errno hidden in asm.

This fixes the build after the -Bsymbolic change.

Bug: 16853291
Change-Id: I989c9fec3c32e0289ea257a3bd2b7fd2709b6ce2
diff --git a/libc/arch-x86/syscalls/geteuid.S b/libc/arch-x86/syscalls/geteuid.S
index 8290a93..469f9c9 100644
--- a/libc/arch-x86/syscalls/geteuid.S
+++ b/libc/arch-x86/syscalls/geteuid.S
@@ -2,6 +2,8 @@
 
 #include <private/bionic_asm.h>
 
+    .hidden __set_errno
+
 ENTRY(geteuid)
     movl    $__NR_geteuid32, %eax
     int     $0x80