kbuild: Do not clutter output with make -jN

Added a new rule filechk used to check when a generated file
actually is changed. If there is no actual changes the file
is left without updating the timestamp.
When building a kernel from scratch two printouts occurs:
  CHK      file-to-generate
  UPD      file-to-generate

The first line tell that kbuild checks the file, second line tell that
the file is being updated (or created).
On successive runs only the first line is printed.
Output is the same in verbose and non-verbose mode.

This replaces the former update-if-changed which has been deleted.
generate-asm-offsets.h has been renamed as well.
All users are updated in next patch.
Output when generating compile.h follow above style

Makefile

@@ -478,17 +478,19 @@ include/linux/autoconf.h: .config scripts/fixdep
 
 uts_len := 64
 
-include/linux/version.h: Makefile
-	@if expr length "$(KERNELRELEASE)" \> $(uts_len) >/dev/null ; then \
+define filechk_version.h
+	if expr length "$(KERNELRELEASE)" \> $(uts_len) >/dev/null ; then \
 	  echo '"$(KERNELRELEASE)" exceeds $(uts_len) characters' >&2; \
 	  exit 1; \
 	fi;
-	@echo -n '  GEN     $@'
-	@(echo \#define UTS_RELEASE \"$(KERNELRELEASE)\"; \
+	(echo \#define UTS_RELEASE \"$(KERNELRELEASE)\"; \
 	  echo \#define LINUX_VERSION_CODE `expr $(VERSION) \\* 65536 + $(PATCHLEVEL) \\* 256 + $(SUBLEVEL)`; \
 	 echo '#define KERNEL_VERSION(a,b,c) (((a) << 16) + ((b) << 8) + (c))'; \
-	) > $@.tmp
-	@$(update-if-changed)
+	)
+endef
+
+include/linux/version.h: Makefile
+	$(call filechk,version.h)
 
 # ---------------------------------------------------------------------------
 
@@ -557,7 +559,7 @@ endif # CONFIG_MODULES
 # Generate asm-offsets.h 
 # ---------------------------------------------------------------------------
 
-define generate-asm-offsets.h
+define filechk_gen-asm-offsets
 	(set -e; \
 	 echo "#ifndef __ASM_OFFSETS_H__"; \
 	 echo "#define __ASM_OFFSETS_H__"; \
@@ -573,7 +575,6 @@ define generate-asm-offsets.h
 	 echo "#endif" )
 endef
 
-
 else # ifdef include_config
 
 ifeq ($(filter-out $(noconfig_targets),$(MAKECMDGOALS)),)
@@ -881,13 +882,27 @@ if_changed_rule = $(if $(strip $? \
 
 cmd = @$(if $($(quiet)cmd_$(1)),echo '  $($(quiet)cmd_$(1))' &&) $(cmd_$(1))
 
-define update-if-changed
-	if [ -r $@ ] && cmp -s $@ $@.tmp; then \
-		echo ' (unchanged)'; \
-		rm -f $@.tmp; \
-	else \
-		echo ' (updated)'; \
-		mv -f $@.tmp $@; \
+# filechk is used to check if the content of a generated file is updated.
+# Sample usage:
+# define filechk_sample
+#	echo $KERNELRELEASE
+# endef
+# version.h : Makefile
+#	$(call filechk,sample)
+# The rule defined shall write to stdout the content of the new file.
+# The existing file will be compared with the new one.
+# - If no file exist it is created
+# - If the content differ the new file is used
+# - If they are equal no change, and no timestamp update
+
+define filechk
+	@echo '  CHK     $@';
+	@set -e; $(filechk_$(1)) > $@.tmp
+	if [ -r $@ ] && cmp -s $@ $@.tmp; then	\
+		rm -f $@.tmp;			\
+	else					\
+		echo '  UPD     $@';		\
+		mv -f $@.tmp $@;		\
 	fi
 endef
 

init/Makefile

@@ -21,5 +21,5 @@ $(obj)/version.o: include/linux/compile.h
 # actual file if its content has changed.
 
 include/linux/compile.h: FORCE
-	@echo -n '  GEN     $@'
+	@echo '  CHK     $@'
 	@sh $(srctree)/scripts/mkcompile_h $@ "$(UTS_MACHINE)" "$(CONFIG_SMP)" "$(CC) $(CFLAGS)"

scripts/mkcompile_h

@@ -10,7 +10,7 @@ CC=$4
 # do "compiled by root"
 
 if [ -r $TARGET -a ! -O include/linux/autoconf.h ]; then
-  echo ' (not modified)'
+  echo "  SKIPPED $TARGET"
   exit 0
 fi
 
@@ -70,10 +70,9 @@ if [ -r $TARGET ] && \
       grep -v 'UTS_VERSION\|LINUX_COMPILE_TIME' $TARGET > .tmpver.1 && \
       grep -v 'UTS_VERSION\|LINUX_COMPILE_TIME' .tmpcompile > .tmpver.2 && \
       cmp -s .tmpver.1 .tmpver.2; then
-   echo ' (unchanged)'
    rm -f .tmpcompile
 else
-   echo ' (updated)'
+   echo "  UPD     $TARGET"
    mv -f .tmpcompile $TARGET
 fi
-#rm -f .tmpver.1 .tmpver.2
+rm -f .tmpver.1 .tmpver.2