CONFIGURE: Avoid needless overwrite of header and mk files

They trigger extensive rebuild of source files without a reason every time
the configure script changes, even if the result is exactly the same.

.gitignore

@@ -15,6 +15,7 @@ lib*.a
 /ScummVMDockTilePlugin*
 /config.h
 /config.mk
+/configure.stamp
 /.gdb_history
 /dumps
 /Credits.rtf

Makefile

@@ -100,7 +100,7 @@ ifneq ($(SAVED_PKG_CONFIG_LIBDIR),unset)
 endif
 
 # check if configure has been run or has been changed since last run
-config.h: $(srcdir)/configure $(ENGINE_SUBDIRS_CONFIGURE)
+configure.stamp: $(srcdir)/configure $(ENGINE_SUBDIRS_CONFIGURE)
 ifeq "$(findstring config.mk,$(MAKEFILE_LIST))" "config.mk"
 	@echo "Running $(srcdir)/configure with the last specified parameters"
 	@sleep 2
@@ -111,12 +111,10 @@ else
 	$(error You need to run $(srcdir)/configure before you can run make. Check $(srcdir)/configure --help for a list of parameters)
 endif
 
-config.mk engines/plugins_table.h engines/engines.mk: config.h
+config.h config.mk engines/plugins_table.h engines/detection_table.h engines/engines.mk: configure.stamp
-	@if test -f $@; then \
+	@if ! test -f $@; then \
-		touch $@; \
+		rm -f configure.stamp; \
-	else \
+		$(MAKE) configure.stamp; \
-		rm -f config.h; \
-		$(MAKE) config.h; \
 	fi
 
 ifneq ($(origin port_mk), undefined)

configure

@@ -941,6 +941,15 @@ get_subengines_build_string() {
 	echo "$subengine_string"
 }
 
+# Copy first argument to second one if they are different. Otherwise, delete the first one.
+copy_if_changed() {
+	if cmp -s $1 $2; then
+		rm -f $1
+	else
+		mv -f $1 $2
+	fi
+}
+
 #
 # Check any parameters we received
 #
@@ -6273,7 +6282,7 @@ fi
 
 echo
 echo "Creating config.h"
-cat > config.h << EOF
+cat > config.h.new << EOF
 /* This file is automatically generated by configure */
 /* DO NOT EDIT MANUALLY */
 
@@ -6306,9 +6315,11 @@ typedef $type_ptr  uintptr;
 
 #endif /* CONFIG_H */
 EOF
+copy_if_changed config.h.new config.h
+
 
 echo "Creating config.mk"
-cat > config.mk << EOF
+cat > config.mk.new << EOF
 # -------- Generated by configure -----------
 
 SAVED_CONFIGFLAGS       := $SAVED_CONFIGFLAGS
@@ -6384,6 +6395,7 @@ $_mak_plugins
 
 port_mk = $_port_mk
 EOF
+copy_if_changed config.mk.new config.mk
 
 #
 # Create a custom Makefile when building outside the source tree
@@ -6392,7 +6404,7 @@ EOF
 if test ! -f Makefile.common ; then
 echo "Creating Makefile"
 
-cat > Makefile << EOF
+cat > Makefile.new << EOF
 # -------- Generated by configure -----------
 srcdir = $_srcdir
 vpath %.h \$(srcdir)
@@ -6407,6 +6419,7 @@ vpath %.rc \$(srcdir)
 vpath %.md \$(srcdir)
 include \$(srcdir)/Makefile
 EOF
+copy_if_changed Makefile.new Makefile
 
 fi
 
@@ -6415,7 +6428,7 @@ fi
 mkdir -p engines
 
 echo "Creating engines/engines.mk"
-cat > engines/engines.mk << EOF
+cat > engines/engines.mk.new << EOF
 # This file is automatically generated by configure
 # DO NOT EDIT MANUALLY
 # This file is being included by "Makefile.common"
@@ -6425,7 +6438,7 @@ for engine in $_sorted_engines; do
 	j=`echo $engine | tr '[:lower:]' '[:upper:]'`
 	if test "`get_engine_sub $engine`" = "no" ; then
 		# main engine
-		cat >> engines/engines.mk << EOF
+		cat >> engines/engines.mk.new << EOF
 
 ifdef ENABLE_$j
 DEFINES += -DENABLE_$j=\$(ENABLE_$j)
@@ -6434,7 +6447,7 @@ EOF
 
 	for subeng in `get_engine_subengines $engine` ; do
 		k=`echo $subeng | tr '[:lower:]' '[:upper:]'`
-		cat >> engines/engines.mk << EOF
+		cat >> engines/engines.mk.new << EOF
 
 ifdef ENABLE_$k
 DEFINES += -DENABLE_$k
@@ -6442,17 +6455,18 @@ endif
 EOF
 	done
 
-	cat >> engines/engines.mk << EOF
+	cat >> engines/engines.mk.new << EOF
 endif
 EOF
 	fi
 done
+copy_if_changed engines/engines.mk.new engines/engines.mk
 
 # Name which is suffixed to each detection plugin
 detectId="_DETECTION"
 
 echo "Creating engines/detection_table.h"
-cat > engines/detection_table.h << EOF
+cat > engines/detection_table.h.new << EOF
 /* This file is automatically generated by configure */
 /* DO NOT EDIT MANUALLY */
 // This file is being included by "base/plugins.cpp"
@@ -6462,17 +6476,18 @@ for engine in $_sorted_engines; do
 	if test "`get_engine_sub $engine`" = "no" ; then
 		j=`echo $engine | tr '[:lower:]' '[:upper:]'`
 		detectEngine="${j}${detectId}"
-		cat >> engines/detection_table.h << EOF
+		cat >> engines/detection_table.h.new << EOF
 #if defined(ENABLE_$j) || defined(DETECTION_FULL)
 LINK_PLUGIN($detectEngine)
 #endif
 EOF
 	fi
 done
+copy_if_changed engines/detection_table.h.new engines/detection_table.h
 
 
 echo "Creating engines/plugins_table.h"
-cat > engines/plugins_table.h << EOF
+cat > engines/plugins_table.h.new << EOF
 /* This file is automatically generated by configure */
 /* DO NOT EDIT MANUALLY */
 // This file is being included by "base/plugins.cpp"
@@ -6481,10 +6496,13 @@ EOF
 for engine in $_sorted_engines; do
 	if test "`get_engine_sub $engine`" = "no" ; then
 		j=`echo $engine | tr '[:lower:]' '[:upper:]'`
-		cat >> engines/plugins_table.h << EOF
+		cat >> engines/plugins_table.h.new << EOF
 #if PLUGIN_ENABLED_STATIC($j)
 LINK_PLUGIN($j)
 #endif
 EOF
 	fi
 done
+copy_if_changed engines/plugins_table.h.new engines/plugins_table.h
+
+touch configure.stamp