[configure] Definition for plugin directories being built

configure.in

@@ -754,35 +754,38 @@ AC_ARG_ENABLE(external,
 
 AC_FOREACH([__plugin],m4_esyscmd([ls src/plugins]),
   [ m4_if(m4_index(KNOWN_SRC_DIRS,__plugin),[-1],
-      [ m4_syscmd(test -r src/plugins/__plugin/configure.in)
+      [
+        m4_define([plugin_dir],[src/plugins/__plugin])
+        m4_syscmd(test -r plugin_dir/configure.in)
         m4_define([is_configure_in],m4_sysval)
-        m4_syscmd(test -r src/plugins/__plugin/configure.ac)
+        m4_syscmd(test -r plugin_dir/configure.ac)
         m4_define([is_configure_ac],m4_sysval)
         m4_define([config_file],
-          [m4_if(is_configure_in,0,src/plugins/__plugin/configure.in,
-             m4_if(is_configure_ac,0,src/plugins/__plugin/configure.ac,no))])
+          [m4_if(is_configure_in,0,plugin_dir/configure.in,
+             m4_if(is_configure_ac,0,plugin_dir/configure.ac,no))])
         m4_if(config_file,[no],
-          [ m4_syscmd(test -r src/plugins/__plugin/Makefile)
+          [ m4_syscmd(test -r plugin_dir/Makefile)
             m4_if(m4_sysval,[0],
               [ m4_syscmd(test "$DISTRIB_CONF" = "yes" && \
                            grep -q -e "PLUGIN_DISTRIBUTED *:= *no" \
-                                src/plugins/__plugin/Makefile
+                                plugin_dir/Makefile
                            )
                 m4_if(m4_sysval,[0],,
-                      [ check_plugin(__plugin,src/plugins/__plugin,
+                      [ check_plugin(__plugin,plugin_dir,
                          [support for __plugin plug-in],yes,yes)
                       if test "$[ENABLE_]tovarname(__plugin)" != "no"; then
-                         EXTERNAL_PLUGINS="$EXTERNAL_PLUGINS src/plugins/__plugin";
+                         EXTERNAL_PLUGINS="$EXTERNAL_PLUGINS plugin_dir";
                       fi])])],
           [ m4_syscmd(test "$DISTRIB_CONF" = "yes" && \
                       grep -q -e "PLUGIN_DISTRIBUTED:=no" \
-                            src/plugins/__plugin/Makefile.in)
+                            plugin_dir/Makefile.in)
             m4_if(m4_sysval,[0],,
-              [ m4_define([plugin_prefix],src/plugins/__plugin)
+              [ m4_define([plugin_prefix],plugin_dir)
                 m4_include(config_file)
-                m4_syscmd(cd src/plugins/__plugin && \
+                m4_syscmd(cd plugin_dir && \
                           [FRAMAC_SHARE]=../../../share autoconf)])
           ])
+        m4_undefine([plugin_dir])
       ])
   ])