configure: avoid touching "config.h" if no change

original commit: a4a9630e90b82113bcfd448d90efd555ffdba636

configure

@@ -534,7 +534,7 @@ sed -e "s;^m=none\$;m=$m;"\
     -e "s;^InstallLZ4Target=.*$;InstallLZ4Target=$installlz4target;"\
     makefiles/Mf-install.in > $w/Mf-install
 
-cat > $w/c/config.h << END
+cat > $w/c/next_config.h << END
 #define SCHEME_SCRIPT "$installscriptname"
 #ifndef WIN32
 #define DEFAULT_HEAP_PATH "$installlib/csv%v/%m"
@@ -542,18 +542,26 @@ cat > $w/c/config.h << END
 END
 
 if [ "$disablex11" = "yes" ]; then
-  echo '#define DISABLE_X11' >> $w/c/config.h
+  echo '#define DISABLE_X11' >> $w/c/next_config.h
 fi
 
 cursesLib=-lcurses
 ncursesLib=-lncurses
 
 if [ "$disablecurses" = "yes" ]; then
-  echo '#define DISABLE_CURSES' >> $w/c/config.h
+  echo '#define DISABLE_CURSES' >> $w/c/next_config.h
   cursesLib=
   ncursesLib=
 fi
 
+if [ ! -f "$w/c/config.h" ] ; then
+   mv $w/c/next_config.h $w/c/config.h
+elif [ `cmp -s $w/c/next_config.h $w/c/config.h`] ; then
+   mv $w/c/next_config.h $w/c/config.h
+else
+   rm $w/c/next_config.h
+fi
+
 warningFlags="-Wpointer-arith -Wall -Wextra -Werror -Wno-implicit-fallthrough"
 optFlags=-O2