docker-proxy: Force external linking to add BuildID information to please rpm

Signed-off-by: Tibor Vass <tibor@docker.com>
(cherry picked from commit 9a690d3544563bf3b88708dabd5bc853e0e749d2)
Signed-off-by: Tibor Vass <tibor@docker.com>

hack/make/dynbinary-daemon

@@ -11,5 +11,6 @@ set -e
 	source "${MAKEDIR}/.binary"
 	export BINARY_SHORT_NAME='docker-proxy'
 	export SOURCE_PATH='./vendor/src/github.com/docker/libnetwork/cmd/proxy'
+	export LDFLAGS_STATIC_DOCKER='-linkmode=external'
 	source "${MAKEDIR}/.binary"
 )