os: add ModeCharDevice to ModeType

When masking FileInfo.Mode() from a character device with the ModeType
mask, ModeCharDevice cannot be recovered.

ModeCharDevice was added https://golang.org/cl/5531052, but nothing
indicates why it was omitted from ModeType. Add it now.

Fixes #27640

Change-Id: I52f56108b88b1b0a5bc6085c66c3c67e10600619
Reviewed-on: https://go-review.googlesource.com/135075
Run-TryBot: Tobias Klauser <tobias.klauser@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

api/except.txt

@@ -3,6 +3,7 @@ pkg math/big, const MaxBase = 36
 pkg math/big, type Word uintptr
 pkg net, func ListenUnixgram(string, *UnixAddr) (*UDPConn, error)
 pkg os, const ModeType = 2399141888
+pkg os, const ModeType = 2399666176
 pkg os (linux-arm), const O_SYNC = 4096
 pkg os (linux-arm-cgo), const O_SYNC = 4096
 pkg syscall (darwin-386), const ImplementsGetwd = false

src/os/types.go

@@ -57,7 +57,7 @@ const (
 	ModeIrregular                                  // ?: non-regular file; nothing else is known about this file
 
 	// Mask for the type bits. For regular files, none will be set.
-	ModeType = ModeDir | ModeSymlink | ModeNamedPipe | ModeSocket | ModeDevice | ModeIrregular
+	ModeType = ModeDir | ModeSymlink | ModeNamedPipe | ModeSocket | ModeDevice | ModeCharDevice | ModeIrregular
 
 	ModePerm FileMode = 0777 // Unix permission bits
 )