hw/xen: Rename xen_common.h to xen_native.h

This header is now only for native Xen code, not PV backends that may be
used in Xen emulation. Since the toolstack libraries may depend on the
specific version of Xen headers that they pull in (and will set the
__XEN_TOOLS__ macro to enable internal definitions that they depend on),
the rule is that xen_native.h (and thus the toolstack library headers)
must be included *before* any of the headers in include/hw/xen/interface.

Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
Reviewed-by: Paul Durrant <paul@xen.org>

include/hw/xen/xen.h

@@ -8,15 +8,21 @@
 #define QEMU_HW_XEN_H
 
 /*
- * As a temporary measure while the headers are being untangled, define
- * __XEN_TOOLS__ here before any Xen headers are included. Otherwise, if
- * the Xen toolstack library headers are later included, they will find
- * some of the "internal" definitions missing and the build will fail. In
- * later commits, we'll end up with a rule that the native libraries have
- * to be included first, which will ensure that the libraries get the
- * version of Xen libraries that they expect.
+ * C files using Xen toolstack libraries will have included those headers
+ * already via xen_native.h, and having __XEM_TOOLS__ defined will have
+ * automatically set __XEN_INTERFACE_VERSION__ to the latest supported
+ * by the *system* Xen headers which were transitively included.
+ *
+ * C files which are part of the internal emulation, and which did not
+ * include xen_native.h, may need this defined so that the Xen headers
+ * imported to include/hw/xen/interface/ will expose the appropriate API
+ * version.
+ *
+ * This is why there's a rule that xen_native.h must be included first.
  */
-#define __XEN_TOOLS__ 1
+#ifndef __XEN_INTERFACE_VERSION__
+#define __XEN_INTERFACE_VERSION__ 0x00040e00
+#endif
 
 #include "exec/cpu-common.h"