There doesn't seem to be much sense in defaulting "on" unwind tables on
amd64 and not on other arches. It causes surprising differences between
platforms, such as the PR below.
Prior to this change, FreeBSD inherited the default implementation of the
method from the Gnu.h Generic_Elf => Generic_GCC parent class, which
returned true only for amd64 targets. Override that and opt on always,
similar to, e.g., NetBSD's driver.
A simple test case for a !amd64 architecture is added to the "freebsd.c"