3 years into the future... :O
from fbuild.builders.pkg_config import PkgConfig
from fbuild.builders.c import guess_static
def build(ctx):
gtk = PkgConfig(ctx, 'gtk+-2.0') # Get the Gtk+ 2 package
c = guess_static(ctx, flags=gtk.cflags, external_libs=gtk.libs)
# etc.
As for Qt: I don't use it, so this may be wrong, but you can use pkg-config as shown above to get the proper flags and implement some sort of moc builder following the implementation of builders/bison.py.