see lib/libarch/Makefile - it includes the subdirs always, and then they
decide what sources to add.  So I'd suggest pruning less aggressively.

As for LD_LIBRARY_PATH getting stripped, the NetBSD view, more or less,
is that having to set it is a sign of a broken installation, and also
build.sh intends to be repeatable.  So this isn't totally surprising,
even though it's a messy problem.