[PATCH] tools: don't use = after "define" in Rules.mk

[Jan Beulich <jbeulich@xxxxxxxx>]

The assignment operator is optional, and use of it breaks with make 3.81.

Fixes: ded08cdfa72b ("tools: generate most contents of library make variables")
Suggested-by: Juergen Gross <jgross@xxxxxxxx>
Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>

--- a/tools/Rules.mk
+++ b/tools/Rules.mk
@@ -94,7 +94,7 @@ INSTALL_DIR_ROOT = [ $$UID -ne 0 ] || $(
 # Consumers of libfoo should not directly use $(SHDEPS_libfoo) or
 # $(SHLIB_libfoo)
 
-define LIB_defs =
+define LIB_defs
  XEN_libxen$(1) = $$(XEN_ROOT)/tools/libs/$(1)
  CFLAGS_libxen$(1) = -I$$(XEN_libxen$(1))/include $$(CFLAGS_xeninclude)
  SHDEPS_libxen$(1) = $$(foreach use,$$(USELIBS_$(1)),$$(SHLIB_libxen$$(use)))