build: correct gas --noexecstack check

The check was missing an escape for the inner $, thus breaking things
in the unlikely event that the underlying assembler doesn't support this
option.

Fixes: 62d22296a9 ("build: silence GNU ld warning about executable stacks")
Signed-off-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Anthony PERARD <anthony.perard@citrix.com>
master commit: d1f6a58dfd
master date: 2023-08-14 09:58:19 +0200

xen/Makefile

@@ -405,7 +405,7 @@ endif
 
 AFLAGS += -D__ASSEMBLY__
 
-$(call cc-option-add,AFLAGS,CC,-Wa$(comma)--noexecstack)
+$(call cc-option-add,AFLAGS,CC,-Wa$$(comma)--noexecstack)
 
 LDFLAGS-$(call ld-option,--warn-rwx-segments) += --no-warn-rwx-segments