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/load_plugins.c

@@ -37,7 +37,7 @@
 /* We always use the same name for the sudoers plugin, regardless of the OS */
 #define SUDOERS_PLUGIN	"sudoers.so"
 
-#ifdef _PATH_SUDO_PLUGIN_DIR
+#ifdef ENABLE_SUDO_PLUGIN_API
 static int
 sudo_stat_plugin(struct plugin_info *info, char *fullpath,
     size_t pathsize, struct stat *sb)
@@ -144,7 +144,7 @@ sudo_check_plugin(struct plugin_info *info, char *fullpath, size_t pathsize)
     (void)strlcpy(fullpath, info->path, pathsize);
     debug_return_bool(true);
 }
-#endif /* _PATH_SUDO_PLUGIN_DIR */
+#endif /* ENABLE_SUDO_PLUGIN_API */
 
 /*
  * Load the plugin specified by "info".