coq 8.1pl2 is out - works for me on x86-64. Also, please change "make" to "emake" on line 54 - parallel make does work for me, so I think MAKE_OPTS should be used.
bumped thanks. though emake -j$alot wouldn't work with the depends system, so I've used -j1 for make alldepend and emake for the rest of the build. it is compatible with ocaml 3.10, though it needs camlp5 recycling the bug to a keywording req for sparc: you're the only arch that don't have dev-ml/camlp5 ~arch keyworded, for now it's fine but when it'll be time to unmask ocaml 3.10, coq will force you to downgrade ocaml. (as a side note, if you upgrade from any version of ocaml to 3.10, make sure you rebuilt the ocaml packages that had been built with older versions)
~sparc keyword added. I note that dev-lang/ocaml-3.10.0 and dev-ml/camlp5-5.01 both build as expected (after a lot of package.unmask'ing). Once those are installed, coq-8.1_p2 builds and installs fine with FEATURES=test --- sparc looks good for this complete combination (and I'm going to have to figure out what coq is about --- looks fascinating).