build: fix %.s: %.S rule

Fixes: e321576f40 ("xen/build: start using if_changed")
Signed-off-by: Anthony PERARD <anthony.perard@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
master commit: d468f95221
master date: 2021-07-05 16:47:51 +0200

xen/Rules.mk

@@ -227,8 +227,8 @@ cmd_cpp_i_c = $(CPP) $(filter-out -Wa$(comma)%,$(c_flags)) -MQ $@ -o $@ $<
 quiet_cmd_cc_s_c = CC      $@
 cmd_cc_s_c = $(CC) $(filter-out -Wa$(comma)%,$(c_flags)) -S $< -o $@
 
-quiet_cmd_s_S = CPP     $@
-cmd_s_S = $(CPP) $(filter-out -Wa$(comma)%,$(a_flags)) -MQ $@ -o $@ $<
+quiet_cmd_cpp_s_S = CPP     $@
+cmd_cpp_s_S = $(CPP) $(filter-out -Wa$(comma)%,$(a_flags)) -MQ $@ -o $@ $<
 
 %.i: %.c FORCE
 	$(call if_changed,cpp_i_c)