From 61f52a04ef4df1c8ba17ebf75baaa25e88b90342 Mon Sep 17 00:00:00 2001
From: Kean Johnston <kean@isc.org>
Date: Thu, 7 Nov 2013 08:38:42 +0200
Subject: [PATCH] [3119] Added a comment regarding autoconf macros used.

As per review added a comment about the use of $ac_header_preproc.
---
 configure.ac | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/configure.ac b/configure.ac
index 4438cbbef4..19be1fd090 100644
--- a/configure.ac
+++ b/configure.ac
@@ -754,6 +754,12 @@ CPPFLAGS_SAVED=$CPPFLAGS
 CPPFLAGS="$BOTAN_INCLUDES $CPPFLAGS"
 LIBS_SAVED="$LIBS"
 LIBS="$LIBS $BOTAN_LIBS"
+
+dnl ac_header_preproc is an autoconf symbol (undocumented but stable) that
+dnl is set if the pre-processor phase passes. Thus by adding a custom
+dnl failure handler we can detect the difference between a header no existing
+dnl (or not even passing the pre-processor phase) and a header file resulting
+dnl in compilation failures.
 AC_CHECK_HEADERS([botan/botan.h],,[
 if test "x$ac_header_preproc" = "xyes"; then
   AC_MSG_ERROR([