pidgin/pidgin

Set the C standard to C99 and set warning_level to 2 for the IRCv3 Protocol Plugin

Testing Done:
Compiled and verified the warnings were gone.

I left the capabilities warnings for now as I'm fixing them in another review request.

Reviewed at https://reviews.imfreedom.org/r/2097/
syntax: glob
.*.swp
.DS_Store
.flatpak-builder
*.pyc
*~
\#*\#
syntax: regexp
^build(.+)?\/
win32-install-dir(\.release)?
po\/pidgin\.pot$
^subprojects\/.+\/