tools: make qemu build use correct PYTHON version

Pass --python=$(PYTHON) to qemu's configure.
Fixes error:
Python not found. Use --python=/path/to/python

Signed-off-by: Christoph Egger <Christoph.Egger@amd.com>
Acked-by: Ian Jackson <ian.jackson@eu.citrix.com>
Committed-by: Ian Jackson <ian.jackson@eu.citrix.com>

tools/Makefile

@@ -155,6 +155,7 @@ subdir-all-qemu-xen-dir subdir-install-qemu-xen-dir: qemu-xen-dir-find
 		-L$(XEN_ROOT)/tools/xenstore" \
 		--bindir=$(LIBEXEC) \
 		--disable-kvm \
+		--python=$(PYTHON) \
 		$(IOEMU_CONFIGURE_CROSS); \
 	$(MAKE) install