tccgen/32bits: fix unsigned long long -> int cast

tccgen/32bits: fix unsigned long long -> int cast

gen_cast() failed to truncate long long's if they
were unsigned, which was causing mess on the vstack.

There was a similar bug here
    tccgen: 32bits: fix PTR +/- long long
    ed15cddacd145c74e4600af50f6616ba59ca0d8d

Both were not visible until this patch
    tccgen: arm/i386: save_reg_upstack
    b691585785086024549cfb9ac65f3397263965aa

I'd still assume that this patch is correct per se.

Also:
- remove 2x !nocode_wanted (we are already under a general
  "else if (!nocode_wanted)" clause above).