After being stuck using gcc 3.4.5 for a very, very long time, the MinGW developers have released a "prerelease" build of gcc 4.2.1. After some basic smoke testing, this version of gcc appears to work fine for building MAME, minus a couple of minor warnings which have been cleared up for the next release. The Development Tools page has now been updated with a fresh package of build tools and links to all the components.

If you download these tools now, you should still be able to build MAME, but you will need to disable -Werror with any version of MAME prior to 0.118u5 (which is not yet released), since there are some new warnings which need to be dealt with (really, not that many).