Do not overwrite config.h unless it was changed. Mostly taken from FFmpeg.

git-svn-id: svn://svn.mplayerhq.hu/mplayer/trunk@24241 b3059339-0415-0410-9bf9-f77b7e298cf2

configure

@@ -1298,6 +1298,7 @@ rm -f "$TMPLOG"
 TMPC="$I/mplayer-conf-$RANDOM-$$.c"
 TMPCPP="$I/mplayer-conf-$RANDOM-$$.cpp"
 TMPEXE="$I/mplayer-conf-$RANDOM-$$"
+TMPH="$I/mplayer-conf-$RANDOM-$$.h"
 TMPS="$I/mplayer-conf-$RANDOM-$$.S"
 
 echo configuration: $_configuration > "$TMPLOG"
@@ -7708,7 +7709,7 @@ done
 }
 
 echo "Creating config.h"
-cat > config.h << EOF
+cat > $TMPH << EOF
 /* -------- This file has been automatically generated by configure ---------
    Note: Any changes in it will be lost when you run configure again. */
 
@@ -8420,6 +8421,9 @@ $_def_xshape
 #endif /* MPLAYER_CONFIG_H */
 EOF
 
+# Do not overwrite an unchanged config.h to avoid superfluous rebuilds.
+! cmp -s "$TMPH" config.h && mv -f "$TMPH" config.h
+
 #############################################################################
 
 cat << EOF
@@ -8512,4 +8516,4 @@ EOF
 fi
 
 # Last move:
-rm -f "$TMPEXE" "$TMPC" "$TMPS" "$TMPCPP"
+rm -f "$TMPEXE" "$TMPC" "$TMPS" "$TMPCPP" "$TMPH"