!157 增加vfork支持

Merge pull request !157 from jesven/vfork

components/lwp/arch/arm/cortex-a/lwp_gcc.S

@@ -94,8 +94,10 @@ lwp_get_user_sp:
     mov pc, lr
 
 .global sys_fork
+.global sys_vfork
 .global sys_fork_exit
 sys_fork:
+sys_vfork:
     push {r4 - r12, lr}
     bl _sys_fork
 sys_fork_exit:

components/lwp/lwp_syscall.c

@@ -1436,6 +1436,7 @@ static int lwp_copy_files(struct rt_lwp *dst, struct rt_lwp *src)
 }
 
 int sys_fork(void);
+int sys_vfork(void);
 void sys_fork_exit(void);
 int _sys_fork(void)
 {
@@ -3203,6 +3204,7 @@ const static void* func_table[] =
     (void *)sys_rename,			/* 135 */
     (void *)sys_fork,
     (void *)sys_execve,
+    (void *)sys_vfork,
 };
 
 const void *lwp_get_sys_api(rt_uint32_t number)