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.

src/parse_args.c

@@ -441,7 +441,7 @@ parse_args(int argc, char **argv, int *nargc, char ***nargv,
 	SET(flags, (MODE_IMPLIED_SHELL | MODE_SHELL));
 	sudo_settings[ARG_IMPLIED_SHELL].value = "true";
     }
-#ifdef _PATH_SUDO_PLUGIN_DIR
+#ifdef ENABLE_SUDO_PLUGIN_API
     sudo_settings[ARG_PLUGIN_DIR].value = sudo_conf_plugin_dir_path();
 #endif