cgen error when spawn anon functions, with closure parameters and mut ref function parameters

[shove70]

Describe the bug

import net

fn main() {
	mut conn := &net.TcpConn{}
	a := 1

	spawn fn [a] (mut conn net.TcpConn) {
	}(mut conn)
}

Reproduction Steps

/tmp/v_501/a.2665062129621293191.tmp.c:2158:50: error: expected identifier or '('
typedef struct thread_arg___v_void_net__TcpConn* {
                                                 ^
/tmp/v_501/a.2665062129621293191.tmp.c:2161:3: error: must use 'struct' tag to refer to type 'thread_arg___v_void_net__TcpConn'
} thread_arg___v_void_net__TcpConn*;
  ^
  struct 
/tmp/v_501/a.2665062129621293191.tmp.c:2161:36: error: expected identifier or '('
} thread_arg___v_void_net__TcpConn*;
                                   ^
/tmp/v_501/a.2665062129621293191.tmp.c:2162:29: error: expected ';' after top level declarator
 void* __v_void_net__TcpConn*_thread_wrapper(thread_arg___v_void_net__TcpConn* *arg);
...
==================
(Use `v -cg` to print the entire error message)

builder error: 
==================
C error. This should never happen.

This is a compiler bug, please report it using `v bug file.v`.

https://github.com/vlang/v/issues/new/choose

You can also use #help on Discord: https://discord.gg/vlang

Expected Behavior

compile passed.

Current Behavior

error.

Possible Solution

No response

Additional Information/Context

No response

V version

latest master

Environment details (OS name and version, etc.)

macos, centos8

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