pidgin/pidgin

Use LT_LIB_M to determine if we need to link to the math library and link Pidgin to the X11 libraries

Gentoo ran into an issue with the gold linker without -lm. The original patch
and work came from Justin Lechner. https://bugs.gentoo.org/386079

Gentoo also ran into an issue with X11_LIBS not being added to pidgin. This
should already be implicit everywhere except for homebrew which patches X11
out of their build. Original patch/work came from and. https://bugs.gentoo.org/500762

Testing Done:
Installed and ran locally.

Reviewed at https://reviews.imfreedom.org/r/608/
/** @page gtklog-signals GtkLog Signals
@signals
@signal log-displaying
@endsignals
@see gtklog.h
<hr>
@signaldef log-displaying
@signalproto
void (*log_displaying)(PidginLogViewer *viewer, PurpleLog *log);
@endsignalproto
@signaldesc
Emitted when a log is being displayed.
@param viewer The log viewer
@param log The log being displayed
@endsignaldef
*/
// vim: syntax=c.doxygen tw=75 et