x86/build: limit rebuilding of asm-offsets.h

This file has a long dependencies list (through asm-offsets.[cs]) and a
long list of dependents. IOW if any of the former changes, all of the
latter will be rebuilt, even if there's no actual change to the
generated file. This is the primary scenario we have the move-if-changed
macro for.

Since debug information may easily cause the file contents to change in
benign ways, also avoid emitting this into the output file.

Finally already before this change *.new files needed including in what
gets removed by the "clean" target.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Roger Pau Monné <roger.pau@citrix.com>

xen/arch/x86/Makefile

@@ -241,7 +241,8 @@ efi/buildid.o efi/relocs-dummy.o: $(BASEDIR)/arch/x86/efi/built_in.o
 efi/buildid.o efi/relocs-dummy.o: ;
 
 asm-offsets.s: $(TARGET_SUBARCH)/asm-offsets.c $(BASEDIR)/include/asm-x86/asm-macros.h
-	$(CC) $(filter-out -Wa$(comma)% -flto,$(c_flags)) -S -o $@ $<
+	$(CC) $(filter-out -Wa$(comma)% -flto,$(c_flags)) -S -g0 -o $@.new $<
+	$(call move-if-changed,$@.new,$@)
 
 asm-macros.i: CFLAGS-y += -D__ASSEMBLY__ -P
 
@@ -268,7 +269,7 @@ efi/mkreloc: efi/mkreloc.c
 
 .PHONY: clean
 clean::
-	rm -f asm-offsets.s *.lds boot/*.o boot/*~ boot/core boot/mkelf32
+	rm -f asm-offsets.s *.lds *.new boot/*.o boot/*~ boot/core boot/mkelf32
 	rm -f asm-macros.i $(BASEDIR)/include/asm-x86/asm-macros.*
 	rm -f $(BASEDIR)/.xen-syms.[0-9]* boot/.*.d $(BASEDIR)/.xen.elf32
 	rm -f $(BASEDIR)/.xen.efi.[0-9]* efi/*.efi efi/mkreloc