Initial check for libvncserver-config in toplevel Makefile.

diff -r a1c2cede77c7 Makefile
@@ -67,7 +67,7 @@ prep-kernels:
 	for i in $(XKERNELS) ; do $(MAKE) $$i-prep || exit 1; done
 
 .PHONY: install-xen
-install-xen:
+install-xen: checklibvncserver
 	$(MAKE) -C xen install
 
 .PHONY: install-tools

@@ -211,6 +211,25 @@ uninstall:
 	rm -rf $(D)/usr/share/man/man1/xen*
 	rm -rf $(D)/usr/share/man/man8/xen*
 
+ifndef IGNORE_LIBVNCSERVER
+IGNORE_LIBVNCSERVER=0
+endif
+
+.PHONY: checklibnvncserver
+checklibvncserver:
+ifneq ($(IGNORE_LIBVNCSERVER), 1)
+	@sh -c '\
+	if ! libvncserver-config --version > /dev/null 2>&1 ; then \
+	echo "Unable to find libvncserver-config.";\
+	echo -n "You must have the libvncserver development libraries to";\
+	echo " enable vnc in QEMU!";\
+	echo "Set IGNORE_LIBVNCSERVER=1 to ignore.";\
+	exit 1; fi\
+	'
+else
+	@:
+endif
+
 # Legacy targets for compatibility
 .PHONY: linux26
 linux26: