misc/cgo/testcarchive: fix tests in module mode

Updates #30228

Change-Id: I830e3c83416b2e5744f30d1a903a74c50462716b
Reviewed-on: https://go-review.googlesource.com/c/163210
Run-TryBot: Bryan C. Mills <bcmills@google.com>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Jay Conrod <jayconrod@google.com>

misc/cgo/testcarchive/testdata/libgo/libgo.go

@@ -0,0 +1,53 @@
+// Copyright 2015 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package main
+
+import (
+	"fmt"
+	"os"
+	"syscall"
+	"time"
+
+	_ "testcarchive/p"
+)
+
+import "C"
+
+var initCh = make(chan int, 1)
+var ranMain bool
+
+func init() {
+	// emulate an exceedingly slow package initialization function
+	time.Sleep(100 * time.Millisecond)
+	initCh <- 42
+}
+
+func main() { ranMain = true }
+
+//export DidInitRun
+func DidInitRun() bool {
+	select {
+	case x := <-initCh:
+		if x != 42 {
+			// Just in case initCh was not correctly made.
+			println("want init value of 42, got: ", x)
+			syscall.Exit(2)
+		}
+		return true
+	default:
+		return false
+	}
+}
+
+//export DidMainRun
+func DidMainRun() bool { return ranMain }
+
+//export CheckArgs
+func CheckArgs() {
+	if len(os.Args) != 3 || os.Args[1] != "arg1" || os.Args[2] != "arg2" {
+		fmt.Printf("CheckArgs: want [_, arg1, arg2], got: %v\n", os.Args)
+		os.Exit(2)
+	}
+}