If BFD_TARG_64 is defined, set BFD_ARCH_SIZE to 64 even on 32-bit platforms.
(BFD_ARCH_SIZE is an attribute of the target, not (just) the host platform)
This is intended for building 32bit->64bit cross libbfd's (e.g.,
x86->alpha or x86->sparc64)
- no includes are installed any more, nor any .a libraries
- a unified libbfd can be built if BFD_UNIFIED is set in mk.conf (will
support dumping/examining objects from all NetBSD architectures of equal
or lesser pointer size)