vendor: add github.com/prometheus/client_golang/prometheus

Signed-off-by: Gary Kim <gary@garykim.dev>

vendor/github.com/prometheus/procfs/internal/util/sysreadfile_compat.go

@@ -0,0 +1,26 @@
+// Copyright 2019 The Prometheus Authors
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// +build linux,appengine !linux
+
+package util
+
+import (
+	"fmt"
+)
+
+// SysReadFile is here implemented as a noop for builds that do not support
+// the read syscall. For example Windows, or Linux on Google App Engine.
+func SysReadFile(file string) (string, error) {
+	return "", fmt.Errorf("not supported on this platform")
+}