on the setting of ${SHLIBDIR} and ${SHLIBINSTALLDIR} (_not_ ${_LIBSODIR}).
Fixes cruel and unusual ^W^W^W obscure native-build and not-so-obscure
cross-builds problems I was having with shared libraries with a
non-base LIBDIR (e.g, /usr/X11R6/lib) that use LDADD to pull in other
libraries from /usr/lib (such as libm) which are really in /lib and the
symlink from ${DESTDIR}/usr/lib/libm.so to /lib/libm.so.N.M was confusing
the linker. Stuffing -rpath-link ${DESTDIR}/lib in solves the problem.
This should mean that shared libraries that depend upon other shared
libraries in other directories should DTRT in a DESTDIR (cross-)build...
Inspired by _PROGLDOPTS in <bsd.prog.mk>
58d2d9a196