Right now there is a possibility to specify "lib.dirs" variable variable in a TEST.properties file to indicate with libraries to compile before executing any test in the hierarchy on the level or below the TEST.properties file.

This cause the whole library to be compiled, which works fine in many cases. However, compilation of the whole library may be unnecessary, and, in some cases, inappropriate (see JDK-8148859).

Jon:
I could image a variant that takes type names instead of or as well as packages, much as @build take take typr of package args. That might lead one to suggest
   lib.build= <stuff>
where <stuff> is the stuff you would put after @build if you were using standard jtreg test descriptions.