tccgen: nocode_wanted: do not output constants

tccgen: nocode_wanted: do not output constants

This for example suppresses string constants such as with

    int main()
    {
        return sizeof "foo";
    }

Actually, setting

    nocode_wanted = 1;

in libtcc.c for the initial global level seemed wrong, since
obviously "nocode_wanted" means code as any side effects, also
such as string constants.

This reverts a part of 2de1b2d14cc920e2c698ff0086f5558c2da7f569
(documented as "Some in-between fixes" in Changelog)