All subconfigures are essentially doing it already, so just inverse the process. That would also limit problems with additional subconfigures (all the recent ones had to come with their own config.cache)
Before, we would run configure in both top-level and js/src, and both
configures would traverse their own set of moz.builds, without actual
knowledge about the other. With this change, both configures still run,
but only top-level traverses moz.build files, and uses js/src's
config.status when traversing its moz.build files. This allows a better
sharing of information between both build systems and the removal of many
hacks.
This also moves running libffi and icu configure to top-level.
Standalone js builds still have their own configure doing moz.build traversal,
as before.
--HG--
rename : config/autoconf.mk.in => config/autoconf-js.mk.in
rename : config/emptyvars.mk.in => config/emptyvars-js.mk.in
