examples: add linux build tag to uretprobe, ringbuf, socket_dist

The two examples call into package unix which is not available
on non-Unix platforms. Add build tags so that

    GOOS=windows go build ./...

works without errors.

Signed-off-by: Lorenz Bauer <[email protected]>

Author: lmb

example_sock_extract_dist_test.go

@@ -1,3 +1,5 @@
+//go:build linux
+
 package ebpf_test
 
 // This code is derived from https://github.com/cloudflare/cloudflare-blog/tree/master/2018-03-ebpf

examples/ringbuffer/bpf_bpfeb.go

@@ -1,3 +1,5 @@
+//go:build linux
+
 package main
 
 import (
@@ -9,13 +11,14 @@ import (
 	"os/signal"
 	"syscall"
 
+	"golang.org/x/sys/unix"
+
 	"github.com/cilium/ebpf/link"
 	"github.com/cilium/ebpf/ringbuf"
 	"github.com/cilium/ebpf/rlimit"
-	"golang.org/x/sys/unix"
 )
 
-//go:generate go run github.com/cilium/ebpf/cmd/bpf2go -type event bpf ringbuffer.c -- -I../headers
+//go:generate go run github.com/cilium/ebpf/cmd/bpf2go -tags linux -type event bpf ringbuffer.c -- -I../headers
 
 func main() {
 	// Name of the kernel function to trace.

examples/ringbuffer/bpf_bpfel.go

@@ -2,7 +2,7 @@
 // The program will be attached to the 'readline' symbol in the binary '/bin/bash' and print out
 // the line which 'readline' functions returns to the caller.
 
-//go:build amd64
+//go:build amd64 && linux
 
 package main
 
@@ -15,13 +15,14 @@ import (
 	"os/signal"
 	"syscall"
 
+	"golang.org/x/sys/unix"
+
 	"github.com/cilium/ebpf/link"
 	"github.com/cilium/ebpf/perf"
 	"github.com/cilium/ebpf/rlimit"
-	"golang.org/x/sys/unix"
 )
 
-//go:generate go run github.com/cilium/ebpf/cmd/bpf2go -target amd64 -type event bpf uretprobe.c -- -I../headers
+//go:generate go run github.com/cilium/ebpf/cmd/bpf2go -target amd64 -tags linux -type event bpf uretprobe.c -- -I../headers
 
 const (
 	// The path to the ELF binary containing the function to trace.