configure.ac: guard docs behind an option

Currently, docs are automatically build, if doxygen is being found. This
should be an option, as in Gentoo, we want to control this via use flag,
if someone wants to have docs, even, if doxygen is installed.

Default is still being yes, so it can be optionally disbled.

Signed-off-by: Conrad Kostecki <conikost@gentoo.org>

configure.ac

@@ -47,6 +47,13 @@ AC_ARG_WITH(contrib, AS_HELP_STRING([--without-contrib], [disable inclusion of c
 if test "x$with_contrib" != "xno"; then
 	AC_DEFINE_UNQUOTED(HAVE_CONTRIB, [1], [Defined if contributed sources are enabled.])
 fi
+AC_ARG_WITH(docs, AS_HELP_STRING([--without-docs], [disable generation of docs]), [], [with_docs=yes])
+if test "x$with_docs" != "xno"; then
+	AC_CHECK_PROGS([HAVE_DOXYGEN], [doxygen], [])
+	if test -z "${HAVE_DOXYGEN}"; then
+        	AC_MSG_WARN([Doxygen not found - continuing without Doxygen support.])
+	fi
+fi
 AC_ARG_WITH(mqtt, AS_HELP_STRING([--without-mqtt], [disable support for MQTT handling]), [], [with_mqtt=yes])
 if test "x$with_mqtt" != "xno"; then
 	AC_CHECK_LIB([mosquitto], [mosquitto_lib_init],
@@ -154,12 +161,8 @@ if test -n "$GIT_REVISION"; then
 else
 	AC_DEFINE(REVISION, "[m4_esyscmd_s([git describe --always 2>/dev/null || (date +p%Y%m%d)])]", [The revision of the package.])
 fi
-AC_CHECK_PROGS([HAVE_DOXYGEN], [doxygen], [])
-if test -z "$HAVE_DOXYGEN"; then
-	AC_MSG_WARN([Doxygen not found - continuing without Doxygen support.])
-fi
 
-AM_CONDITIONAL([HAVE_DOXYGEN], [test -n "$HAVE_DOXYGEN"])
+AM_CONDITIONAL([HAVE_DOXYGEN], [test -n "${HAVE_DOXYGEN}"])
 AM_COND_IF([HAVE_DOXYGEN], [AC_CONFIG_FILES([docs/Doxyfile])])
 
 AM_INIT_AUTOMAKE([1.11 -Wall -Werror foreign subdir-objects])