[PATCH] configure.ac: warn about unknown '--with-' / '--enable-' options

[slyfox inbox ru]

From: Sergei Trofimovich <slyfox gentoo org>

As we use 'AC_CONFIG_SUBDIRS' macro for samba sources
option checking is disabled for us.

Before the patch:

    $ ./configure --with-i-have-misspelled-editor-for-edit
    ...
    # no warnings

The patch enables warnings back only for top-level ./configure:

    $ ./configure --with-i-have-misspelled-editor-for-edit
    ...
    configure: WARNING: unrecognized options: --with-i-have-misspelled-editor-for-edit

Signed-off-by: Sergei Trofimovich <slyfox gentoo org>
---
 configure.ac | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/configure.ac b/configure.ac
index c12c2e7..5581a14 100644
--- a/configure.ac
+++ b/configure.ac
@@ -652,3 +652,12 @@ Configuration:
   Support for charset:        ${charset_msg}
   Search type:                ${SEARCH_TYPE}
 ])
+
+dnl option checking is disable by default due to AC_CONFIG_SUBDIRS
+dnl we enable it back for top-level ./configure
+if test -n "$ac_unrecognized_opts"; then
+  case $enable_option_checking in
+    fatal) AC_MSG_ERROR([unrecognized options: $ac_unrecognized_opts]) ;;
+    *)     AC_MSG_WARN( [unrecognized options: $ac_unrecognized_opts]) ;;
+  esac
+fi
-- 
1.8.2.1