Since metaconfig units are modular, you don't have to regenerate perl5's entire
Configure every time you want to test just one unit.  Instead, you can 
run metaconfig against a smaller project that tests just one (or a few)
units.  That's what this U.check directory is for.

Just edit main.c and dummy.SH to use whatever metaconfig symbols you're
trying to test.  Then run  metaconfig -m  to regenerate Configure.
You'll get a slimmed-down Configure that tests just what you want to test.
