My GCC does not support the -msse4.1 switch. It should be detected in configure before trying to use it, for example with the AX_CHECK_COMPILE_FLAG macro from the autoconf archive.
This was added in commit 6f2e81ce4cc by Matt Turner.
-msse4.1 has existed in gcc since 4.3. 4.3 was released five and a half years ago. Why are you using something older than that?
Sounds like you've got a good idea how to solve it. Send a patch and I'll review it.
Originally to be compatible with the BSDs and Mac, now it's just convenient for building binaries that run on any distro (with newer GCCs requiring newer libstdc++).
I think it would be fair for you to fix it since you broke it ;) but sure, I'll provide a patch this week.
Committed your patch. Thanks