A new version of openMSX is out Reproducible: Always Steps to Reproduce: 1. 2. 3.
Needs dev-lang/tcl-8.4 so until that's stable there will be a delay, at least from me. The build system has completely changed since the last release as well so an ebuild rewrite looks to be in order.
A new ebuild is out, with patches to take control of the new build system. It does not yet listen to CFLAGS in /etc/make.conf, but it should build and be usable. Please let me know how you get on with it. Thanks for your report :)