prometheus: set build info via x-flags

Similar to `syncthing` also `prometheus` build environment sets
variables later shown in the `--version` string. Set those varialbes.

Signed-off-by: Paul Spooren <mail@aparcar.org>

utils/prometheus/Makefile

@@ -2,7 +2,7 @@ include $(TOPDIR)/rules.mk
 
 PKG_NAME:=prometheus
 PKG_VERSION:=2.20.1
-PKG_RELEASE:=1
+PKG_RELEASE:=2
 
 PKG_SOURCE:=$(PKG_NAME)-$(PKG_VERSION).tar.gz
 PKG_SOURCE_URL:=https://codeload.github.com/prometheus/prometheus/tar.gz/v${PKG_VERSION}?
@@ -19,6 +19,13 @@ PKG_USE_MIPS16:=0
 GO_PKG:=github.com/prometheus/prometheus/
 GO_PKG_BUILD_PKG:=github.com/prometheus/prometheus/cmd/prometheus/
 
+GO_PKG_LDFLAGS_X:=\
+	github.com/prometheus/common/version.Version=v$(PKG_VERSION) \
+	github.com/prometheus/common/version.Revision=$(PKG_VERSION)  \
+	github.com/prometheus/common/version.Branch="release" \
+	github.com/prometheus/common/version.BuildUser=openwrt \
+	github.com/prometheus/common/version.BuildDate=$(SOURCE_DATE_EPOCH)
+
 include $(INCLUDE_DIR)/package.mk
 include ../../lang/golang/golang-package.mk