when you installed google-go-lang have you logged out from your root shell and logged in again (or become root with "su -", note the leading dash) before building what depended on it?
the google-go-lang stuff is added to your environment via /etc/profile.d/* scripts (that are sourced in login shells), it's explained in its README.
what is the output of
EDIT: no, the problem was actually another: see this
gentoo bug
just add a line to the SlackBuild
Code:
--- a/system/docker-machine-kvm/docker-machine-kvm.SlackBuild
+++ b/system/docker-machine-kvm/docker-machine-kvm.SlackBuild
@@ -80,6 +80,9 @@ find -L . \
mkdir -p build/src/github.com/dhiltgen
ln -sf $TMP/$PRGNAM-$VERSION build/src/github.com/dhiltgen/$PRGNAM
+# https://bugs.gentoo.org/893080
+sed -e 's: -i::' -i cmd/docker-machine-driver-kvm/Makefile
+
export GO111MODULE="off"
make -C cmd/docker-machine-driver-kvm \
GOPATH=$TMP/$PRGNAM-$VERSION/build
thanks for the report!