fix build with make 3.81

make 3.81 doesn't support multiline variables defined with

 define var =
 ...
 endef

Dropping the "=" in the first line will fix the issue.

Fixes: ded08cdfa7 ("tools: generate most contents of library make variables")
Fixes: ddb2934a91 ("stubdom: add correct dependencies for Xen libraries")
Reported-by: Jan Beulich <jbeulich@suse.com>
Signed-off-by: Juergen Gross <jgross@suse.com>
Reviewed-by: Ian Jackson <ian.jackson@eu.citrix.com>

stubdom/Makefile

@@ -25,7 +25,7 @@ endif
 
 include $(XEN_ROOT)/tools/libs/uselibs.mk
 
-define LIB_deps =
+define LIB_deps
  LIBDEPS_$(1) = $$(foreach use,$$(USELIBS_$(1)),libxen$$(use))
 endef
 $(foreach lib,$(LIBS_LIBS),$(eval $(call LIB_deps,$(lib))))