The default if-found action of AC_CHECK_LIB is to add the library to LIBS,

but that means it's used for all linking. So a GPL-compliant libgadu gets

linked with libpurple, finch, pidgin, and all plugins instead of just the

protocol plugin.

Compiled and checked that there was no libgadu.so in ldd libpurple.so and a few other built things, but it was still there for the Gadu-Gadu protocol plugin.