windows: add LockFileEx, UnlockFileEx system calls

Changes in syscall_windows.go were copied from
internal/syscall/syscall_windows.go.

zsyscall_windows.go was regenerated by running
'go generate -tags=generate golang.org/x/sys/windows'
using a toolchain built from tip (after CL 196122).

These functions are called by cmd/go/internal/lockedfile via
internal/syscall/windows. I'd like to copy lockedfile into another
project (CL 197299), but these functions need to be exposed here in
order to do so. We may need these in x/mod eventually, too.

Change-Id: I2033106d2ba65009e764591bfe5702f4d41dffdd
Reviewed-on: https://go-review.googlesource.com/c/sys/+/198060
Run-TryBot: Jay Conrod <jayconrod@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Jason A. Donenfeld <Jason@zx2c4.com>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-by: Alex Brainman <alex.brainman@gmail.com>

Author: Jay Conrod

windows/syscall_windows.go

@@ -57,6 +57,10 @@ const (
 	FILE_VOLUME_IS_COMPRESSED         = 0x00008000
 	FILE_VOLUME_QUOTAS                = 0x00000020
 
+	// Flags for LockFileEx.
+	LOCKFILE_FAIL_IMMEDIATELY = 0x00000001
+	LOCKFILE_EXCLUSIVE_LOCK   = 0x00000002
+
 	// Return values of SleepEx and other APC functions
 	STATUS_USER_APC    = 0x000000C0
 	WAIT_IO_COMPLETION = STATUS_USER_APC
@@ -160,6 +164,8 @@ func NewCallbackCDecl(fn interface{}) uintptr {
 //sys	DeleteFile(path *uint16) (err error) = DeleteFileW
 //sys	MoveFile(from *uint16, to *uint16) (err error) = MoveFileW
 //sys	MoveFileEx(from *uint16, to *uint16, flags uint32) (err error) = MoveFileExW
+//sys	LockFileEx(file Handle, flags uint32, reserved uint32, bytesLow uint32, bytesHigh uint32, overlapped *Overlapped) (err error)
+//sys	UnlockFileEx(file Handle, reserved uint32, bytesLow uint32, bytesHigh uint32, overlapped *Overlapped) (err error)
 //sys	GetComputerName(buf *uint16, n *uint32) (err error) = GetComputerNameW
 //sys	GetComputerNameEx(nametype uint32, buf *uint16, n *uint32) (err error) = GetComputerNameExW
 //sys	SetEndOfFile(handle Handle) (err error)