Update Go build

* Update Go to 1.21.
* Update minimum Go version to 1.20.
* Remove obsolete extra build flgas.

Fixes: #1005

Signed-off-by: SuperQ <[email protected]>

Author: SuperQ

.circleci/config.yml

@@ -5,7 +5,7 @@ executors:
   # Whenever the Go version is updated here, .promu.yml should also be updated.
   golang:
     docker:
-      - image: cimg/go:1.20
+      - image: cimg/go:1.21
 jobs:
   test:
     executor: golang
@@ -23,7 +23,7 @@ jobs:
     # Whenever the Go version is updated here, .travis.yml and .promu.yml
     # should also be updated.
     environment:
-      DOCKER_TEST_IMAGE_NAME: quay.io/prometheus/golang-builder:1.20-base
+      DOCKER_TEST_IMAGE_NAME: quay.io/prometheus/golang-builder:1.21-base
     steps:
       - checkout
       - run:

.promu.yml

@@ -1,11 +1,9 @@
 go:
-    # Whenever the Go version is updated here, .travis.yml and
-    # .circle/config.yml should also be updated.
-    version: 1.20
+    # Whenever the Go version is updated here, .circle/config.yml should also be updated.
+    version: 1.21
 repository:
     path: github.com/prometheus/blackbox_exporter
 build:
-    flags: -a -tags netgo
     ldflags: |
         -X github.com/prometheus/common/version.Version={{.Version}}
         -X github.com/prometheus/common/version.Revision={{.Revision}}

go.mod

@@ -1,6 +1,6 @@
 module github.com/prometheus/blackbox_exporter
 
-go 1.19
+go 1.20
 
 require (
 	github.com/alecthomas/kingpin/v2 v2.4.0