Cross build Promtail for ARM with journald support.

This is the follow up to grafana#8111 and adds journald support for Promatil
ARM and ARM64 builds.

I've tested it locally with my Raspberry Pi and it works.

Fixes grafana#1459

Makefile

@@ -251,7 +251,9 @@ dist: clean
 	CGO_ENABLED=0 $(GOX) -osarch="linux/amd64 linux/arm64 linux/arm darwin/amd64 darwin/arm64 windows/amd64 freebsd/amd64" ./cmd/loki
 	CGO_ENABLED=0 $(GOX) -osarch="linux/amd64 linux/arm64 linux/arm darwin/amd64 darwin/arm64 windows/amd64 freebsd/amd64" ./cmd/logcli
 	CGO_ENABLED=0 $(GOX) -osarch="linux/amd64 linux/arm64 linux/arm darwin/amd64 darwin/arm64 windows/amd64 freebsd/amd64" ./cmd/loki-canary
-	CGO_ENABLED=0 $(GOX) -osarch="linux/arm64 linux/arm darwin/amd64 darwin/arm64 windows/amd64 windows/386 freebsd/amd64" ./clients/cmd/promtail
+	CGO_ENABLED=0 $(GOX) -osarch="darwin/amd64 darwin/arm64 windows/amd64 windows/386 freebsd/amd64" ./clients/cmd/promtail
+	PKG_CONFIG_PATH="/usr/lib/aarch64-linux-gnu/pkgconfig" CC="aarch64-linux-gnu-gcc" $(CGO_GOX)  -tags promtail_journal_enabled  -osarch="linux/arm64" ./clients/cmd/promtail
+	PKG_CONFIG_PATH="/usr/lib/arm-linux-gnueabihf/pkgconfig" CC="arm-linux-gnueabihf-gcc" $(CGO_GOX)  -tags promtail_journal_enabled  -osarch="linux/arm" ./clients/cmd/promtail
 	CGO_ENABLED=1 $(CGO_GOX) -osarch="linux/amd64" ./clients/cmd/promtail
 	for i in dist/*; do zip -j -m $$i.zip $$i; done
 	pushd dist && sha256sum * > SHA256SUMS && popd