str_intp: autofree memory leak fix 1

[kbkpbot]

This PR try to fix memory leak cause by str_intp().

leak.v:

struct Test {
        a string
}

fn main() {
        cmd1 := 'ls'
        cmd2 := 'rm'
        _ := Test {
                a : 'cmd ${cmd1} ${cmd2} failed'
        }
}

without autofree, generate c:

VV_LOCAL_SYMBOL void main__main(void) {
        string cmd1 = _SLIT("ls");
        string cmd2 = _SLIT("rm");
        {main__Test _ = ((main__Test){.a = str_intp(3, _MOV((StrIntpData[]){{_SLIT("cmd "), 0xfe10, {.d_s = cmd1}}, {_SLIT(" "), 0xfe10, {.d_s = cmd2}}, {_SLIT(" failed"), 0, { .d_c = 0 }}})),});}
        ;
}

with autofree, generate c:

VV_LOCAL_SYMBOL void main__main(void) {
        string cmd1 = _SLIT("ls");
        string cmd2 = _SLIT("rm");
        string _t1 = str_intp(3, _MOV((StrIntpData[]){{_SLIT("cmd "), 0xfe10, {.d_s = cmd1}}, {_SLIT(" "), 0xfe10, {.d_s = cmd2}}, {_SLIT(" failed"), 0, { .d_c = 0 }}}));
        {main__Test _ = ((main__Test){.a = _t1,});}
        ;
        string_free(&_t1); // autofreed var main false
        string_free(&cmd2); // autofreed var main false
        string_free(&cmd1); // autofreed var main false
}

and run valgrind will get a clean result.

valgrind --error-exitcode=1 --leak-check=full --show-reachable=yes ./leak

==510777== Memcheck, a memory error detector
==510777== Copyright (C) 2002-2022, and GNU GPL'd, by Julian Seward et al.
==510777== Using Valgrind-3.22.0 and LibVEX; rerun with -h for copyright info
==510777== Command: ./leak
==510777==
==510777==
==510777== HEAP SUMMARY:
==510777==     in use at exit: 0 bytes in 0 blocks
==510777==   total heap usage: 3 allocs, 3 frees, 274 bytes allocated
==510777==
==510777== All heap blocks were freed -- no leaks are possible
==510777==
==510777== For lists of detected and suppressed errors, rerun with: -s
==510777== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 0 from 0)
#-gc boehm_leak

[huly-for-github]

Connected to Huly®: V_0.6-21977

[kbkpbot]

It seems conflict to fn call args autofree, fix later...