tools/include/Makefile: Support `build' target

This is the only one of the Makefiles invoked with -C from the
toplevel which lacks this target.

CC: Wei Liu <wei.liu2@citrix.com>
Signed-off-by: Ian Jackson <Ian.Jackson@eu.citrix.com>
Tested-by: M A Young <m.a.young@durham.ac.uk>
Tested-by: Andrew Cooper <andrew.cooper3@citrix.com>
Release-acked-by: Julien Grall <julien.grall@arm.com>

tools/include/Makefile

@@ -4,8 +4,8 @@ include $(XEN_ROOT)/tools/Rules.mk
 # Relative to $(XEN_ROOT)/xen/xsm/flask
 FLASK_H_DEPEND := policy/initial_sids
 
-.PHONY: all
-all: xen-foreign xen/.dir xen-xsm/.dir
+.PHONY: all build
+all build: xen-foreign xen/.dir xen-xsm/.dir
 
 .PHONY: xen-foreign
 xen-foreign: