bison 3.0.1
Prevent deps of build-time deps from leaking into the build environment

When decided what dependencies should be part of the build environment
(and have appropriate entries added to variables like PKG_CONFIG_PATH),
we select the entire dependency tree except for

 (1) inactive optional and recommended deps (2) indirect build-time deps
 (i.e., build-time deps of other deps)

There is a third category that sould be excluded: dependencies of direct
build-time deps. These are irrelevant to the build, and including them
can cause unexpected linkages.