configure: Added support for --enable-<plugin>=force.

This may be used to force a plugin to be built, no matter what the dependency
check yielded. I.e. this is basically the same --enable-<plugin> before commit
9276a81 (configure.in: Let configure bail out
on missing dependencies).

README

@@ -553,7 +553,10 @@ Configuring / Compiling / Installing
   will be enabled). To enable a plugin, install missing dependencies (see
   section `Prerequisites' above) and rerun `configure'. If you specify the
   `--enable-<plugin>' configure option, the script will fail if the depen-
-  dencies for the specified plugin are not met. If you specify the
+  dencies for the specified plugin are not met. In that case you can force the
+  plugin to be built using the `--enable-<plugin>=force' configure option.
+  This will most likely fail though unless you're working in a very unusual
+  setup and you really know what you're doing. If you specify the
   `--disable-<plugin>' configure option, the plugin will not be built. If you
   specify the `--enable-all-plugins' or `--disable-all-plugins' configure
   options, all plugins will be enabled or disabled respectively by default.

configure.in

@@ -3223,14 +3223,19 @@ AC_DEFUN(
   [AC_PLUGIN],
   [
     enable_plugin="no"
+    force="no"
     AC_ARG_ENABLE([$1], AC_HELP_STRING([--enable-$1], [$3]),
     [
      if test "x$enableval" = "xyes"
      then
 	     enable_plugin="yes"
+     else if test "x$enableval" = "xforce"
+     then
+	     enable_plugin="yes"
+	     force="yes"
      else
 	     enable_plugin="no"
-     fi
+     fi; fi
     ],
     [
 	 if test "x$enable_all_plugins" = "xauto"
@@ -3247,9 +3252,13 @@ AC_DEFUN(
     ])
     if test "x$enable_plugin" = "xyes"
     then
-	    if test "x$2" = "xyes"
+	    if test "x$2" = "xyes" || test "x$force" = "xyes"
 	    then
 		    AC_DEFINE([HAVE_PLUGIN_]my_toupper([$1]), 1, [Define to 1 if the $1 plugin is enabled.])
+		    if test "x$2" != "xyes"
+		    then
+			    dependency_warning="yes"
+		    fi
 	    else # User passed "yes" but dependency checking yielded "no" => Dependency problem.
 		    dependency_error="yes"
 		    enable_plugin="no (dependency error)"
@@ -3267,7 +3276,9 @@ AC_COLLECTD([debug],     [enable],  [feature], [debugging])
 AC_COLLECTD([daemon],    [disable], [feature], [daemon mode])
 AC_COLLECTD([getifaddrs],[enable],  [feature], [getifaddrs under Linux])
 
+dependency_warning="no"
 dependency_error="no"
+
 plugin_ascent="no"
 plugin_battery="no"
 plugin_bind="no"
@@ -3899,7 +3910,11 @@ Configuration:
 EOF
 
 if test "x$dependency_error" = "xyes"; then
-	AC_MSG_ERROR("Some plugins are missing dependencies - see above summary for details")
+	AC_MSG_ERROR("Some plugins are missing dependencies - see the summary above for details")
+fi
+
+if test "x$dependency_warning" = "xyes"; then
+	AC_MSG_WARN("Some plugins seem to have missing dependencies but have been enabled forcibly - see the summary above for details")
 fi
 
 # vim: set fdm=marker :