conf/177845: WITH_BMAKE does not work on CURRENT

[Simon J. Gerraty]

FWIW the buildworld I just did (with freebsd make as /usr/bin/make)
finished ok (tree updated to r249461), and lots of previous builds used 
bmake as /usr/bin/make.  I'll rebuild this same tree that way...

Yep, that complete ok too. 

>	I'm rebuilding world right now so it might be due to a bug fixed =
>in the past, but I swear I've seen this on another CURRENT box I kept =
>reasonably (within the past couple months) up to date.