Convensions for NO_<feature> instead of HAVE_<feature>?

[Hallvard B Furuseth]

I want some code to be semi-independent of Autoconf, and to default
to using <feature> instead of not using it without Autoconf.
#ifdef HAVE_<feature> means that the code will not use <feature>
without autoconf, unless the user defines HAVE_FEATURE by hand.

Are there any conventions for what to call such feature macros and how
to write them in Autoconf?  NO_<feature>?  NEED_<feature>_REPLACEMENT?

-- 
Hallvard