Created attachment 340994 [details, diff] Remove -Wl,-R emerging povray-3.7.0_rc6 on Darwin (Gentoo Prefix) will make ld complain about the -R option and hence boost cannot be detected.
Linking to existing upstream bug/discussion.
Comment on attachment 340994 [details, diff] Remove -Wl,-R The upstream decided to still use -Wl,{-R,-rpath} instead of dropping it like this patch suggests.
+*boost-m4-0.3 (05 Mar 2013) + + 05 Mar 2013; Nathan Phillip Brink <binki@gentoo.org> +boost-m4-0.3.ebuild: + Bump to boost-m4-0.3 which includes a Mac OSX -rpath LDFLAGS fix for bug + #460362. New boost-m4-0.3 to specifically solve this issue. So just update povray to DEPEND=">=sys-devel/boost-m4-0.3" and it should be good. Thanks for the bug report to get this issue moving both here and upstream. Marking RESOLVED immediately because this package is still unstable.
Thanks for your quick response and the fix, I will add the *-macos keywords to boost-m4-0.3 only, so no change to povray will be necessary.