kbuild: move headers_check.pl to usr/include/

This script is only used by usr/include/Makefile. Make it local to
the directory.

Update the comment in include/uapi/linux/soundcard.h because
'make headers_check' is no longer functional.

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

include/uapi/linux/soundcard.h

@@ -1051,7 +1051,7 @@ typedef struct mixer_vol_table {
  *	the GPL version of OSS-4.x and build against that version
  *	of the header.
  *
- *	We redefine the extern keyword so that make headers_check
+ *	We redefine the extern keyword so that usr/include/headers_check.pl
  *	does not complain about SEQ_USE_EXTBUF.
  */
 #define SEQ_DECLAREBUF()		SEQ_USE_EXTBUF()

usr/include/Makefile

@@ -99,10 +99,12 @@ quiet_cmd_hdrtest = HDRTEST $<
       cmd_hdrtest = \
 		$(CC) $(c_flags) -S -o /dev/null -x c /dev/null \
 			$(if $(filter-out $(no-header-test), $*.h), -include $< -include $<); \
-		$(PERL) $(srctree)/scripts/headers_check.pl $(obj) $(SRCARCH) $<; \
+		$(PERL) $(srctree)/$(src)/headers_check.pl $(obj) $(SRCARCH) $<; \
 		touch $@
 
 $(obj)/%.hdrtest: $(obj)/%.h FORCE
 	$(call if_changed_dep,hdrtest)
 
-clean-files += $(filter-out Makefile, $(notdir $(wildcard $(obj)/*)))
+# Since GNU Make 4.3, $(patsubst $(obj)/%/,%,$(wildcard $(obj)/*/)) works.
+# To support older Make versions, use a somewhat tedious way.
+clean-files += $(filter-out Makefile headers_check.pl, $(notdir $(wildcard $(obj)/*)))