Pull sync generated syscalls

This moves all the current users of
$GOROOT/src/syscall/mksyscall_windows.go to instead use
golang.org/x/sys/windows/mkwinsyscall, as directed by the version of the
former in Go 1.15.

It also syncs the local forks of mksyscall_windows.go with the latest
version of golang.org/x/sys/windows/mkwinsyscall/mkwinsyscall.go, so
that the local patches can be easily seen in a side-by-side comparison.
Significant changes compared to the in-tree forked versions:
* *bool parameters are read back through a temp-var, not directly like
  other pointer parameters.
* ?-suffixed function names support testing for function presence before
  calling. This replaces a local implementation of this in
  pkg/security, which was not actually used anyway. The upstream version
  correctly supports functions that don't already have an error return.
* `errnoErr(0)` is now useful, so each call of `errnoErr` doesn't need
  to be protected with a check for 0 first.
* The generated functions are now sorted. This of course produced a
  *lot* of churn in the generated files.

vhd\vhd.go was changed to generate syscalls into zvhd_windows.go, since
regeneration removes the build tag added by hand in
9d8277341f.

After all that, I also ran
```
go generate . .\pkg\etw\ .\pkg\process\ .\pkg\security\ .\vhd\
```
to update all the existing generated code.

Signed-off-by: Paul "TBBle" Hampson <Paul.Hampson@Pobox.com>

vhd/vhd.go

@@ -11,7 +11,7 @@ import (
 	"golang.org/x/sys/windows"
 )
 
-//go:generate go run mksyscall_windows.go -output zvhd.go vhd.go
+//go:generate go run mksyscall_windows.go -output zvhd_windows.go vhd.go
 
 //sys createVirtualDisk(virtualStorageType *VirtualStorageType, path string, virtualDiskAccessMask uint32, securityDescriptor *uintptr, createVirtualDiskFlags uint32, providerSpecificFlags uint32, parameters *CreateVirtualDiskParameters, overlapped *syscall.Overlapped, handle *syscall.Handle) (err error) [failretval != 0] = virtdisk.CreateVirtualDisk
 //sys openVirtualDisk(virtualStorageType *VirtualStorageType, path string, virtualDiskAccessMask uint32, openVirtualDiskFlags uint32, parameters *OpenVirtualDiskParameters, handle *syscall.Handle) (err error) [failretval != 0] = virtdisk.OpenVirtualDisk