build: silence GNU ld warning about executable stacks

While for C files the compiler is supposed to arrange for emitting
respective information, for assembly sources we're responsible ourselves.
Present GNU ld master started warning about such, and hence 2.39 is
anticipated to have this warning.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Andrew Cooper <andrew.cooper3@citrix.com>
Acked-by: Julien Grall <jgrall@amazon.com>

xen/Makefile

@@ -397,6 +397,8 @@ endif
 
 AFLAGS += -D__ASSEMBLY__
 
+$(call cc-option-add,AFLAGS,CC,-Wa$(comma)--noexecstack)
+
 LDFLAGS-$(call ld-option,--warn-rwx-segments) += --no-warn-rwx-segments
 
 CFLAGS += $(CFLAGS-y)