Always define _PATH_SUDO_NOEXEC, _PATH_SUDO_SESH, _PATH_SUDO_PLUGIN_DIR,

even if only defined to NULL.  This means the accessors can always be
present.

Use RTLD_PRELOAD_VAR instead of _PATH_SUDO_NOEXEC to tell when
noexec is available.

Add ENABLE_SUDO_PLUGIN_API and use it instead of _PATH_SUDO_PLUGIN_DIR
to tell when the plugin API is available.

Add sudo_conf_clear_paths() to clear the path values so the
regress tests are not affected by compile-time settings.

plugins/sudoers/policy.c

@@ -256,7 +256,7 @@ sudoers_policy_deserialize_info(void *v, char **runas_user, char **runas_group)
 	    remhost = *cur + sizeof("remote_host=") - 1;
 	    continue;
 	}
-#ifdef _PATH_SUDO_PLUGIN_DIR
+#ifdef ENABLE_SUDO_PLUGIN_API
 	if (MATCHES(*cur, "plugin_dir=")) {
 	    path_plugin_dir = *cur + sizeof("plugin_dir=") - 1;
 	    continue;