Fix ETW package to work on 386

The ETW registration handle is defined to be 64-bits on all platforms. The Go
type previously used a uintptr which created problems on 32-bit systems. This
change adds a new wrapper file which receives a 64-bit handle for the functions
defined in it, and correctly passes it to the native ETW functions either as-is
(on 64-bit) or as two 32-bit values (on 32-bit).

This required a minor change in mksyscall_windows.go, to allow multiple syscalls
that map to the same underlying function without causing a duplicate definition
error in the generated file.

pkg/etw/wrapper_32.go

@@ -0,0 +1,51 @@
+// +build 386 arm
+
+package etw
+
+import (
+	"golang.org/x/sys/windows"
+)
+
+func low(v providerHandle) uint32 {
+	return uint32(v & 0xffffffff)
+}
+
+func high(v providerHandle) uint32 {
+	return low(v >> 32)
+}
+
+func eventUnregister(providerHandle providerHandle) (win32err error) {
+	return eventUnregister_32(low(providerHandle), high(providerHandle))
+}
+
+func eventWriteTransfer(
+	providerHandle providerHandle,
+	descriptor *eventDescriptor,
+	activityID *windows.GUID,
+	relatedActivityID *windows.GUID,
+	dataDescriptorCount uint32,
+	dataDescriptors *eventDataDescriptor) (win32err error) {
+
+	return eventWriteTransfer_32(
+		low(providerHandle),
+		high(providerHandle),
+		descriptor,
+		activityID,
+		relatedActivityID,
+		dataDescriptorCount,
+		dataDescriptors)
+}
+
+func eventSetInformation(
+	providerHandle providerHandle,
+	class eventInfoClass,
+	information uintptr,
+	length uint32) (win32err error) {
+
+	return eventSetInformation_32(
+		low(providerHandle),
+		high(providerHandle),
+		class,
+		information,
+		length)
+}