Add -Wdocumentation if supported by the compiler.

configure.ac

@@ -20,6 +20,9 @@ OBJCFLAGS="$OBJCFLAGS -Wall $($OBJFW_CONFIG --objcflags)"
 LDFLAGS="$LDFLAGS $($OBJFW_CONFIG --ldflags)"
 LIBS="$LIBS $($OBJFW_CONFIG --libs)"
 
+AX_CHECK_COMPILER_FLAGS(-Wdocumentation,
+	[OBJCFLAGS="$OBJCFLAGS -Wdocumentation"])
+
 AC_ARG_ENABLE(shared,
 	AS_HELP_STRING([--disable-shared], [do not build shared library]))
 AS_IF([test x"$enable_shared" != x"no"], [

m4/ax_check_compiler_flags.m4

@@ -0,0 +1,78 @@
+# ===========================================================================
+#        http://autoconf-archive.cryp.to/ax_check_compiler_flags.html
+# ===========================================================================
+#
+# SYNOPSIS
+#
+#   AX_CHECK_COMPILER_FLAGS(FLAGS, [ACTION-SUCCESS], [ACTION-FAILURE])
+#
+# DESCRIPTION
+#
+#   Check whether the given compiler FLAGS work with the current language's
+#   compiler, or whether they give an error. (Warnings, however, are
+#   ignored.)
+#
+#   ACTION-SUCCESS/ACTION-FAILURE are shell commands to execute on
+#   success/failure.
+#
+# LAST MODIFICATION
+#
+#   2008-04-12
+#
+# COPYLEFT
+#
+#   Copyright (c) 2008 Steven G. Johnson <stevenj@alum.mit.edu>
+#   Copyright (c) 2008 Matteo Frigo
+#
+#   This program is free software: you can redistribute it and/or modify it
+#   under the terms of the GNU General Public License as published by the
+#   Free Software Foundation, either version 3 of the License, or (at your
+#   option) any later version.
+#
+#   This program is distributed in the hope that it will be useful, but
+#   WITHOUT ANY WARRANTY; without even the implied warranty of
+#   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General
+#   Public License for more details.
+#
+#   You should have received a copy of the GNU General Public License along
+#   with this program. If not, see <http://www.gnu.org/licenses/>.
+#
+#   As a special exception, the respective Autoconf Macro's copyright owner
+#   gives unlimited permission to copy, distribute and modify the configure
+#   scripts that are the output of Autoconf when processing the Macro. You
+#   need not follow the terms of the GNU General Public License when using
+#   or distributing such scripts, even though portions of the text of the
+#   Macro appear in them. The GNU General Public License (GPL) does govern
+#   all other use of the material that constitutes the Autoconf Macro.
+#
+#   This special exception to the GPL applies to versions of the Autoconf
+#   Macro released by the Autoconf Macro Archive. When you make and
+#   distribute a modified version of the Autoconf Macro, you may extend this
+#   special exception to the GPL to apply to your modified version as well.
+
+AC_DEFUN([AX_CHECK_COMPILER_FLAGS],
+[AC_PREREQ(2.59) dnl for _AC_LANG_PREFIX
+AC_MSG_CHECKING([whether _AC_LANG compiler accepts $1])
+dnl Some hackery here since AC_CACHE_VAL can't handle a non-literal varname:
+AS_LITERAL_IF([$1],
+  [AC_CACHE_VAL(AS_TR_SH(ax_cv_[]_AC_LANG_ABBREV[]_flags_$1), [
+      ax_save_FLAGS=$[]_AC_LANG_PREFIX[]FLAGS
+      _AC_LANG_PREFIX[]FLAGS="$1"
+      AC_COMPILE_IFELSE([AC_LANG_PROGRAM()],
+        AS_TR_SH(ax_cv_[]_AC_LANG_ABBREV[]_flags_$1)=yes,
+        AS_TR_SH(ax_cv_[]_AC_LANG_ABBREV[]_flags_$1)=no)
+      _AC_LANG_PREFIX[]FLAGS=$ax_save_FLAGS])],
+  [ax_save_FLAGS=$[]_AC_LANG_PREFIX[]FLAGS
+   _AC_LANG_PREFIX[]FLAGS="$1"
+   AC_COMPILE_IFELSE([AC_LANG_PROGRAM()],
+     eval AS_TR_SH(ax_cv_[]_AC_LANG_ABBREV[]_flags_$1)=yes,
+     eval AS_TR_SH(ax_cv_[]_AC_LANG_ABBREV[]_flags_$1)=no)
+   _AC_LANG_PREFIX[]FLAGS=$ax_save_FLAGS])
+eval ax_check_compiler_flags=$AS_TR_SH(ax_cv_[]_AC_LANG_ABBREV[]_flags_$1)
+AC_MSG_RESULT($ax_check_compiler_flags)
+if test "x$ax_check_compiler_flags" = xyes; then
+	m4_default([$2], :)
+else
+	m4_default([$3], :)
+fi
+])dnl AX_CHECK_COMPILER_FLAGS