Log Message:
Propagate a fix from NetBSD base bsd.lib.mk: if SHLIB_FULLVERSION is
the same as SHLIB_MAJOR, don't try to symlink SHLIB_MAJOR. Otherwise
you lose the library and get a symlink pointing to itself, and things
fail later with ELOOP.

Fixes builds of packages that use bsd.lib.mk for shared libraries and
set only a major version number.