In the new-style testing configurations, we were hardcoding paths to the
include and lib directories, which was incorrect but always went
unnoticed because the hardcoded values always happened to match the
actual value.
When using new-style configs with the bootstrapping build, this falls
appart -- and we never noticed this because the bootstrapping build was
still using old style configs.
This patch removes the %{install} substitution, which makes it too
tempting to hardcode installation paths, and it also switches the
bootstrapping build to actually using new-style configs like we
always intended to do.