This is a tricky package to support, since the tar file is improperly
structured and it is not an autotools package. Refactor slightly and
add IS_TAR_BOMB option for this kind of use case.
We need to distinguish between tools we compile to use as part of the
build process, and things we build for the eventual target. Install
these into separate install directories; for now, pkg-config is the
only one of these.