Allow the configure process a chance to detect on its own whether the
named library exists or not by allowing those library options to pass
through to the compiler on a test compile. A package that *needs*
those library options to be removed can add the appropriate rm:
BUILDLINK_TRANSFORM command to its package Makefile.
is included by packages that use dlopen(), and dlopen.builtin.mk,
which checks for the presence of built-in dl*() functions. On Darwin,
including dlopen.buildlink3.mk will cause the devel/dlcompat package
to be used if the base system lacks a dlcompat library.
