cgen: Free optional string

[esquerbatua]

Describe the bug

Try to free an structure with a optional string

Reproduction Steps

module main

pub struct Test {
    b ?string
}

fn main() {
    t := Test{
        b: "b"
    }

    println("t: ${t}")

    defer {
        unsafe {
            t.free()
        }
    }
}

Expected Behavior

The program compile and run correctly without errors

Current Behavior

================== C compilation error (from tcc): ==============
cc: /tmp/v_1000/jsonx.01J5G50V9VFVJAHVS165MZ904H.tmp.c:2223: warning: implicit declaration of function '_option_string_free'
cc: /home/esquerbatua/git/v/thirdparty/tcc/lib/libgc.a: error: 'GC_noop1_ptr' defined twice
cc: tcc: error: undefined symbol '_option_string_free'
=================================================================
(You can pass `-cg`, or `-show-c-output` as well, to print all the C error messages).
builder error: 
==================
C error found. It should never happen, when compiling pure V code.
This is a V compiler bug, please report it using `v bug file.v`,
or goto https://github.com/vlang/v/issues/new/choose .
You can also use #help on Discord: https://discord.gg/vlang .

Possible Solution

No response

Additional Information/Context

No response

V version

Current V version: V 0.4.7 e9c9580, timestamp: 2024-08-17 14:34:42 +0300

Environment details (OS name and version, etc.)

V full version: V 0.4.7 4940f2d.e9c9580
OS: linux, Ubuntu 24.04 LTS
Processor: 16 cpus, 64bit, little endian, AMD Ryzen 7 7840HS w/ Radeon 780M Graphics

vexe: /home/esquerbatua/git/v/v
vexe mtime: 2024-08-17 12:30:16

vroot: OK, value: /home/esquerbatua/git/v
VMODULES: OK, value: /home/esquerbatua/.vmodules
VTMP: OK, value: /tmp/v_1000

Git version: git version 2.43.0
Git vroot status: weekly.2024.33-19-ge9c95803
.git/config present: true

CC version: cc (Ubuntu 13.2.0-23ubuntu4) 13.2.0
thirdparty/tcc status: thirdparty-linux-amd64 0134e9b9

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