it fails on a 32bit prefix because strmov has multible definitions, but compiles on a 64bit prefix. In the patch is a workaround (thanks to chithead).
Created attachment 220979 [details, diff] mysql-5.0.90.ebuild.patch
Created attachment 220981 [details] build.log
* On Fedora 12, strmov() did not guarantee correct operation for overlapping source and destination buffer. Calls were fixed to use an overlap-safe version instead. (Bug#48866: http://bugs.mysql.com/bug.php?id=48866)
looks like this commit is around the problem: http://lists.mysql.com/commits/95654 feels like strmov isn't well detected
This is fixed in the 5.1.* versions.