bootstrapped by `make world'. The version just built in ".."
normally won't work if the target system is not binary compatible.
Don't build or install anything if _BUILD_TOOLS is defined. Then
we only want to build and install the colldef binary, but the layout
of the colldef tree forces recursing to colldef/data for at least
the obj target even when _BUILD_TOOLS is defined.
This will make a number of things easier in the future, as well as (finally!)
avoiding the Id-smashing problem which has plagued developers for so long.
Boy, I'm glad we're not using sup anymore. This update would have been
insane otherwise.
