Quoting Richard Guenther <richard.guent...@gmail.com>:
Re-compiling the same plugin sources for different gcc versions is not supported. Of course you might be lucky for minor version changes such as 4.5.3 to 4.5.4.
I think that's putting it a bit too strong. If the maintainer of a plugin cares about the plugin working for a new gcc version that comes out, it is up to that plugin maintainer to determine if any relevant interfaces have changed so that the plugin source needs changing to continue support, or if the plugin simply won't be portable to that gcc version. Once it has been determined that no relevant interface has changed for a plugin, re-compiling it for the new gcc version should work fine. (Well, strictly speaking, it would work or not work regardless of people having found out about this before, but that's not a safe mode to operate.) It's pretty much the same as for out-of-tree patches. They may or may not work in a new version. There's nothing wrong with applying an old patch to a newer gcc version, if you know what you are doing.
