Suggestion: "make help" should print list of configurations

[Martin Buchholz]

I'm having fun with the shiny new build system.
It took me a while to discover that "make help" was exceptionally helpful.

However, I was interested in passing a configuration to CONF= and was
annoyed there was no clue what to provide.  (I wasn't even sure exactly
what a "configuration" was)

After some trial and error, I discovered that

make CONF=bogus

would actually give me that precious list of supported configurations.
It would be nice if "make help" always printed that list, even though by
default it contains only one entry.