Add cfi directives to x86 syscalls.

Modify the syscalls script to generate the cfi directives for x86
syscalls.

Update the x86 syscalls.

Change-Id: Ia1993dc714a7e79f917087fff8200e9a02c52603
diff --git a/libc/arch-x86/syscalls/_exit.S b/libc/arch-x86/syscalls/_exit.S
index 04dc16b..2ff5faf 100644
--- a/libc/arch-x86/syscalls/_exit.S
+++ b/libc/arch-x86/syscalls/_exit.S
@@ -4,6 +4,8 @@
 
 ENTRY(_exit)
     pushl   %ebx
+    .cfi_def_cfa_offset 4
+    .cfi_rel_offset ebx, 0
     mov     8(%esp), %ebx
     movl    $__NR_exit_group, %eax
     int     $0x80