regex.m4: how do I know that the included regex is used?

[Sam Steingold]

Hi,
When the included regex is used I must prepend -I$(srcdir)/gllib to
CPPFLAGS to ensure that the gnulib regex.h is included in the sources.
(when this is not the case, I _must_ not do that!)
This raises 2 questions:

1. how do I know elsewhere in the configuration process that the
   included regex is used? the authoritative variable is
   ac_use_included_regex, but it is not cached, so sub-configures cannot
   access it.

2. what if there is some other gnulib package xeger with the same modus
   operandi? (i.e., if xeger is used, I must prepend -I$(srcdir)/gllib
   to CPPFLAGS and if it is not, I must not).
   what if regex IS used but xeger is NOT?

I propose that regex.h is replaced with regex.in.h just like
fnmatch.in.h (which has no @@ either).  This would solve the problem
without any action from the users of gnulib.

Thanks.

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Sam Steingold (http://sds.podval.org/) on CentOS release 5.6 (Final) X 
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