Created attachment 394176 [details] ebuild for CLHEP-2.2.0.4 there are new versions available for CLHEP. Just copying the 2.2.0.1 ebuild to a local overlay and renaming to 2.2.0.4 did the trick. This new version also fixes a bug with building sci-physics/geant (https://bugs.gentoo.org/show_bug.cgi?id=531042)
2.2.0.5 already in the tree.