bug#17157: [PATCH 1/5] Partially revert "dfa: improve port to freestanding DJGPP"

[Paul Eggert]

Paolo Bonzini wrote:
> setlocale, static_assert etc. should be in a dfacompat.h file

We already have a file that serves this function, called mbsupport.h. 
We could rename it to dfaconfig.h (a better name than dfacompat.h, as 
it's basically a separate config.h for dfa.c).

While we're on the topic, does anybody build gawk or grep with 
-DMBS_SUPPORT=0?  I suspect not, which means we could simplify 
dfaconfig.h compared to mbsupport.h.  (And if somebody does build it 
that way, I suspect it's buggy....)