gnome-common.m4 and gnome-compiler-flags.m4 were taken from version
3.18.0, and match current master branch.

Disable building help and test directories.

Signed-off-by: Eneas U de Queiroz <cote2004-github@yahoo.com>

Version .8 no longer uses Autotools and will thus take a while to be
supported.

Silenced the build from warnings to help fix a bunch of -Wformat ones that
currently break the buildbots.

Explicitly disabled all plugins that are currently unused to save on build
time.

Signed-off-by: Rosen Penev <rosenp@gmail.com>

Signed-off-by: W. Michael Petullo <mike@flyn.org>

Signed-off-by: W. Michael Petullo <mike@flyn.org>