[app-shells/elvish] unecessary dependency on gcc[go]

[nelsam]

The line GOLANG_PACKAGE_USE_CGO seems to force elvish to depend on gcc[go]. Since elvish doesn't need gccgo to run, and cgo isn't exactly the same as gccgo, I think it should be removed.

I forked the project and wrote a fix, but it seems like repoman fix -d doesn't like my funtoo system (I bounce back and forth a lot between funtoo and gentoo). The fix is here