Portability checks
Sizeof int != sizeof size_t
The locale linkage is assuming wchar_t is unicode.

Check this by checking for __STDC_ISO_10646__
Check for backends that know the cell size

If they know they're generating integer cells let the constant folding
do all calculations it can even if they might overflow.
More messing with variations on dlopen.

This time I've got code that should work properly on more historical
versions of Linux because it no longer uses the ISO/POSIX mandated
type punning to pass function pointers around... If nothing else
it eliminates the warnings.

In addition, I've added my understanding of how Linux/ELF shared library
linking works. And more importantly why some odd things work that at
first glance shouldn't.