Installing autotoolset (0.11.4-r1) on my AMD64 system recently lead me to discover that it is unavailable for this system. I have implemented an overlay ebuild for this which does allow amd64, and have done some quick testing of it with no difficulties (gpl, acconfig and acmkdir certainly work fine). Patch to fix this was to simply add ~amd64 (or ideally just amd64) to the KEYWORDS line in the ebuild, and emerge that from my overlay.
Created attachment 75756 [details, diff] Patch for autotoolset-0.11.4-r1.ebuild to enable ~amd64
keyword added thanks for testing btw... no need to write a patch for this kind of bugs :)