hvmloader: don't build with __XEN_TOOLS__ defined

This being an in-guest component, it shouldn't get to see (and even
less so use) tools-only public interfaces.

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>

--- a/tools/firmware/hvmloader/Makefile
+++ b/tools/firmware/hvmloader/Makefile
@@ -31,6 +31,9 @@ SMBIOS_REL_DATE ?= $(shell date +%m/%d/%
 
 CFLAGS += $(CFLAGS_xeninclude)
 
+# We mustn't use tools-only public interfaces.
+CFLAGS += -U__XEN_TOOLS__ -D__XEN_INTERFACE_VERSION__=__XEN_LATEST_INTERFACE_VERSION__
+
 OBJS  = hvmloader.o mp_tables.o util.o smbios.o 
 OBJS += smp.o cacheattr.o xenbus.o vnuma.o
 OBJS += e820.o pci.o pir.o ctype.o