Question on AC_CHECK_HEADERS/AC_DEFINE interaction

[Pádraig Brady]

At line 40 we AC_DEFINE(HAVE_SELINUX_SELINUX_H,0)
  
http://git.savannah.gnu.org/gitweb/?p=gnulib.git;a=blob;f=m4/selinux-selinux-h.m4;h=fd09b299;hb=HEAD#l40
However that may already defined to 1 which is the case
when compiling in -m32 mode but with only the first of these installed:

  $ rpm -qf /usr/include/selinux/selinux.h
  libselinux-devel-2.3-9.fc22.x86_64
  libselinux-devel-2.3-9.fc22.i686

In that edge case, -Werror will fail due to the redefinition,
thus causing -Werror to not be used in the build.

Quite the edge case I know, but I'm not sure how best to avoid.
Perhaps we should not use AC_CHECK_HEADERS here,
instead going lower level with AC_PREPROC_IFELSE(.. AC_DEFINE ..) ?

cheers,
Pádraig.