Fix the exit syscall stub's name.

I've left the exit_group syscall as _exit because otherwise we'd have to
convince the compiler that our _exit (which just calls __exit_group) is
actually "noreturn", and it seems like that would be less clean than just
cutting out the middleman.

We'll just have to trust ourselves not to add anything to SYSCALLS.TXT
that ought to be private but that only has a single leading underscore.
Hopefully we can manage that.

Change-Id: Iac47faea9f516186e1774381846c54cafabc4354
diff --git a/libc/arch-x86/syscalls.mk b/libc/arch-x86/syscalls.mk
index 3b8586b..ade6d55 100644
--- a/libc/arch-x86/syscalls.mk
+++ b/libc/arch-x86/syscalls.mk
@@ -3,6 +3,7 @@
 syscall_src += arch-x86/syscalls/__brk.S
 syscall_src += arch-x86/syscalls/__clone.S
 syscall_src += arch-x86/syscalls/__epoll_pwait.S
+syscall_src += arch-x86/syscalls/__exit.S
 syscall_src += arch-x86/syscalls/__fcntl.S
 syscall_src += arch-x86/syscalls/__fcntl64.S
 syscall_src += arch-x86/syscalls/__fstatfs64.S
@@ -34,7 +35,6 @@
 syscall_src += arch-x86/syscalls/__timer_settime.S
 syscall_src += arch-x86/syscalls/__waitid.S
 syscall_src += arch-x86/syscalls/_exit.S
-syscall_src += arch-x86/syscalls/_exit_thread.S
 syscall_src += arch-x86/syscalls/accept.S
 syscall_src += arch-x86/syscalls/acct.S
 syscall_src += arch-x86/syscalls/bind.S
diff --git a/libc/arch-x86/syscalls/_exit_thread.S b/libc/arch-x86/syscalls/__exit.S
similarity index 90%
rename from libc/arch-x86/syscalls/_exit_thread.S
rename to libc/arch-x86/syscalls/__exit.S
index 1dbac6a..e906ea2 100644
--- a/libc/arch-x86/syscalls/_exit_thread.S
+++ b/libc/arch-x86/syscalls/__exit.S
@@ -4,7 +4,7 @@
 #include <linux/err.h>
 #include <machine/asm.h>
 
-ENTRY(_exit_thread)
+ENTRY(__exit)
     pushl   %ebx
     mov     8(%esp), %ebx
     movl    $__NR_exit, %eax
@@ -19,4 +19,4 @@
 1:
     popl    %ebx
     ret
-END(_exit_thread)
+END(__exit)