This is a follow-up commit to 255ff74f:
building network-manager with Meson breaks users of NetworkManager.pc.

* gnu/packages/messaging.scm (pidgin)[source]: Add pidgin-libnm.patch.
Force re-bootstrapping in a new snippet.
[native-inputs]: Add autoconf, automake, and libtool.
* gnu/packages/patches/pidgin-libnm.patch: New file.
* gnu/local.mk (dist_patch_DATA): Add it.