Now app-emulation/virtualbox-guest-additions is listed in package.mask of features/64bit-native. I have unmasked it and built on amd64 system without an issues. It even works fine. Reproducible: Always
Still works with 4.2.16. See also #476324.
*** Bug 435412 has been marked as a duplicate of this bug. ***
Confirmed for hardened - app-emulation/virtualbox-4.3.26 builds and works fine. Please, unmask (for profiles/hardened/linux/amd64/no-multilib/package.mask).
Hey, package.mask still has app-emulation/virtualbox* while it is compiling and working fine. So, please, remove app-emulation/virtualbox* from profiles/features/64bit-native/package.mask