Log Message:
BUILDLINK_TRANSFORM+= rm:-lXp

This works around the Motif imake templates, which unconditionally
provide -lXp for Motif clients. It is not clear to me why imake
material for Motif is shipped as part of the default X imake templates
rather than with Motif; but imake has always had a special (il)logic
of its own.

Dealing with this problem by setting IMAKEOPTS here instead causes
"can't buildlink files" and I don't understand why; but this approach
is maybe better anyway.

Fixes build of audio/xmradio and perhaps other Motif-using packages.