- everything that has prereq will also do includes, add it late, so that
gnu stuff (the only part with prereq) happens late.
- new RUN_MAKE snippet, to be able to have the makefile magically decide
between Makefile.bsd-wrapper and Makefile.
So there's no longer any need to remember complicated rules: add it to
RDIRS if it just wants make includes, add it to PRDIRS if it wants prereq too,
and that's all.
okay deraadt@, miod@