runtime: import os package in BenchmarkRunningGoProgram

I would like to use BenchmarkRunningGoProgram to measure
changes for issue #15588. So the program in the benchmark
should import "os" package.

It is also reasonable that basic Go program includes
"os" package.

For #15588.

Change-Id: Ida6712eab22c2e79fbe91b6fdd492eaf31756852
Reviewed-on: https://go-review.googlesource.com/37914
Run-TryBot: Alex Brainman <alex.brainman@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

src/runtime/syscall_windows_test.go

@@ -1037,7 +1037,7 @@ func BenchmarkRunningGoProgram(b *testing.B) {
 	defer os.RemoveAll(tmpdir)
 
 	src := filepath.Join(tmpdir, "main.go")
-	err = ioutil.WriteFile(src, []byte(benchmarkRunnigGoProgram), 0666)
+	err = ioutil.WriteFile(src, []byte(benchmarkRunningGoProgram), 0666)
 	if err != nil {
 		b.Fatal(err)
 	}
@@ -1060,9 +1060,11 @@ func BenchmarkRunningGoProgram(b *testing.B) {
 	}
 }
 
-const benchmarkRunnigGoProgram = `
+const benchmarkRunningGoProgram = `
 package main
 
+import _ "os" // average Go program will use "os" package, do the same here
+
 func main() {
 }
 `