prefer_openssl: OSX: get rid of /proc warnings

OSX does not have /proc/cpuinfo, but let's not warn
the user about it.

internal/prefer_openssl/prefer.go

@@ -3,6 +3,7 @@ package prefer_openssl
 import (
 	"io/ioutil"
 	"regexp"
+	"runtime"
 
 	"github.com/rfjakob/gocryptfs/internal/tlog"
 )
@@ -16,9 +17,12 @@ import (
 // filePreferOpenSSL takes an explicit filename so it can be tested with saved
 // cpuinfo files instead of /proc/cpuinfo.
 func filePreferOpenSSL(file string) bool {
+	if runtime.GOOS == "darwin" && file == "/proc/cpuinfo" {
+		// OSX does not have /proc, let's not warn about it.
+		return true
+	}
 	ci, err := ioutil.ReadFile(file)
 	if err != nil {
-		tlog.Warn.Println(err)
 		return true
 	}
 	haveAes, err := regexp.Match(`(?m)^flags.*\baes\b`, ci)