fuse: move parseFuseFd() to unbreak darwin build

Unfortunately, I broke darwin with the last commit:

+ GOOS=darwin
+ GOARCH=amd64
+ go build -tags without_openssl -o /dev/null
../../../../pkg/mod/github.com/hanwen/go-fuse/v2@v2.1.1-0.20210825070001-74a933d6/fuse/server.go:122:5: undefined: parseFuseFd
../../../../pkg/mod/github.com/hanwen/go-fuse/v2@v2.1.1-0.20210825070001-74a933d6/fuse/server.go:887:5: undefined: parseFuseFd

Move parseFuseFd() to build on all archs to unbreak the build.

Change-Id: Ice173cc70a6a95765b56b444623b68ed92382052

fuse/mount_linux.go

@@ -11,7 +11,6 @@ import (
 	"os"
 	"os/exec"
 	"path"
-	"strconv"
 	"strings"
 	"syscall"
 	"unsafe"
@@ -119,20 +118,6 @@ func callFusermount(mountPoint string, opts *MountOptions) (fd int, err error) {
 	return
 }
 
-// parseFuseFd checks if `mountPoint` is the special form /dev/fd/N (with N >= 0),
-// and returns N in this case. Returns -1 otherwise.
-func parseFuseFd(mountPoint string) (fd int) {
-	dir, file := path.Split(mountPoint)
-	if dir != "/dev/fd/" {
-		return -1
-	}
-	fd, err := strconv.Atoi(file)
-	if err != nil || fd <= 0 {
-		return -1
-	}
-	return fd
-}
-
 // Create a FUSE FS on the specified mount point.  The returned
 // mount point is always absolute.
 func mount(mountPoint string, opts *MountOptions, ready chan<- error) (fd int, err error) {

fuse/server.go

@@ -9,8 +9,10 @@ import (
 	"log"
 	"math"
 	"os"
+	"path"
 	"path/filepath"
 	"runtime"
+	"strconv"
 	"strings"
 	"sync"
 	"syscall"
@@ -891,3 +893,17 @@ func (ms *Server) WaitMount() error {
 	}
 	return pollHack(ms.mountPoint)
 }
+
+// parseFuseFd checks if `mountPoint` is the special form /dev/fd/N (with N >= 0),
+// and returns N in this case. Returns -1 otherwise.
+func parseFuseFd(mountPoint string) (fd int) {
+	dir, file := path.Split(mountPoint)
+	if dir != "/dev/fd/" {
+		return -1
+	}
+	fd, err := strconv.Atoi(file)
+	if err != nil || fd <= 0 {
+		return -1
+	}
+	return fd
+}