simpler configure.ac about snappy HOT 4 CLOSED

This won't work. You need to get HAVE_STDINT_H from somewhere; the usual place 
would be config.h, but you cannot include config.h in a public header file, 
since that would pull in definitions (e.g. of VERSION) that would conflict with 
other autotools-based projects' config.h.

In short, the current behavior is correct and needed.

Hum, you're right, thanks for the explanation :)

Looking at snappy.h:

http://code.google.com/p/snappy/source/browse/trunk/snappy.h#42

Unlike snappy-stubs-public.h.in, the inclusion of stddef.h is not conditional.
Isn't this a problem?

stddef.h should always be available (by the C standard), as far as I know, so I 
think the HAVE_ for stddef.h is redundant. The other header isn't.