autofree: memory leak about v

[kbkpbot]

This bug is related to how V(c gen) operate on string.
For example:

VV_LOCAL_SYMBOL void main__leak_test(main__MyLeak* leak) {
        string _t1 = str_intp(1, _MOV((StrIntpData[]){{_SLIT("&"), 0xfe10 ,{.d_s = isnil(leak) ? _SLIT("nil") : main__MyLeak_str(*leak)}}})); println(_t1); string_free(&_t1);
        ;
}

As the function main__MyLeak_str(*leak) will create a new string on heap, but there is noway free it.

I checked the vlib/gen/c/str.v: fn (mut g Gen) gen_expr_to_string(expr ast.Expr, etype ast.Type), it try to generate a string from expr, but this will sometimes alloc a new string on heap.

It need to free somewhere.