Fix x86 cfi directives for syscalls.

The syscall generation always used 4 bytes for each push cfi directive.
However, the first push should always use an offset of 8 bytes, each
subsequent push after that is only 4 bytes though.

Change-Id: Ibaabd107f399ef67010b9a08213783957c2f74a9
diff --git a/libc/arch-x86/syscalls/_exit.S b/libc/arch-x86/syscalls/_exit.S
index 793c9d5..5b569b9 100644
--- a/libc/arch-x86/syscalls/_exit.S
+++ b/libc/arch-x86/syscalls/_exit.S
@@ -4,7 +4,7 @@
 
 ENTRY(_exit)
     pushl   %ebx
-    .cfi_def_cfa_offset 4
+    .cfi_def_cfa_offset 8
     .cfi_rel_offset ebx, 0
     mov     8(%esp), %ebx
     movl    $__NR_exit_group, %eax