* xenial doesn't ship many dependencies, so make them all optional
since we don't guarantee that everything will work
* cmake/{5,6}: needs stdlib.h for EXIT_SUCCESS on GCC 5
* common/222: needs C++11, and GCC 5 doesn't understand `auto`
correctly unless we explicitly enable it.
* frameworks/1 boost: xenial doesn't ship boost_python3, so make it
properly optional
* frameworks/6 gettext: gettext can be installed without xgettext,
which doesn't cause the project to fail, but the installed files
list is different which causes the test to fail.
* frameworks/7 gnome: gobject-introspection can't be enabled because
the sanitizer unit test detects leaks in glib and fails
'if_true' sources should be built with their dependencies, as
illustrated by test case change.
Ideally, I think we would want only the files with the dependencies to
be built with the flags, but that would probably change the way
sourceset are used.
Nirbheek Chauhan
Marc-André Lureau
Jussi Pakkanen
Michael Hirsch, Ph.D
Paolo Bonzini