Never use `int` as fixnums

int usually enough to hold any pointer (void*) on 32-bit machines, but ECL for a while requires support of long long.

The old test decided that int is enough, and ECL can't be bootstraped.

Up to 16.1.3 such error can be avoided by --disable-longdouble but 20.4.24 makes requirement for long long mandatory.

Here I've enforced larger type on 32 bit machines.