AC_SEARCH_LIBS without LIBS

[NightStrike]

AC_SEARCH_LIBS replaced AC_CHECK_LIBS.  The latter had an
action-if-found path that did not unilaterally set $LIBS if you
provided a custom action.  The former always changes $LIBS, even in
the case of custom actions if found.

This is an issue if you need to check for the existence of a library,
but only use it in a subset of all of your things being compiled.

Is this considered a bug in AC_SEARCH_LIBS, or is there a workaround
I'm missing?