Re: new macro: AC_C_RESTRICT

[Paul Eggert]

> > [ __restrict __restrict__ _Restrict ]
> 
> Wow...  There is already that many different names...

These names were all introduced before the C99 standard made
"restrict" official, so I don't expect many more aliases to crop up.

> config.h should encode the result of the system audit only, and not
> the actions.

We could split things up in a backward-compatible way, by having
config.h include (or bodily incorporate) a new file "config-have.h",
which defines only the HAVE_* symbols.  Then people who want the
newer, cleaner semantics could include "config-have.h".