Re-use Allocate/Deallocate for New/Delete, instead of libsupc++ functions

Fixes that part of #699.

I don't think this will cause compatibility issues with FB vs C++.
libsupc++ seems to just call malloc/free anyways, and either way, any code
doing the NEW should also be the code that's doing the DELETE.

Also, FB doesn't support exceptions, so why should it call libsupc++'s
exception throwing new/delete? If at all, FB should have been using the
non-throwing versions, but those also have the extra nothrow parameter.

The good thing about this is that it allows FB's NEW/DELETE to have more
sane behaviour (return NULL on failure, instead of platform-specific
exception throwing/abort/error message), and potentially we can remove
FB's dependency on libsupc++ completely, which would be great because it'd
make FB easier to install on Linux.
Remove the now unused FB_RTL_OPT_OPERATOR
Remove the now unused env.target.size_t32/64
Remove libsupc++ from default libs

(see also 8a950185)