Add multiple inclusion guards to config.h.

Originally committed as revision 10772 to svn://svn.ffmpeg.org/ffmpeg/trunk

configure

@@ -1832,6 +1832,8 @@ echo "Creating config.mak and config.h..."
 
 echo "# Automatically generated by configure - do not modify!" > config.mak
 echo "/* Automatically generated by configure - do not modify! */" > $TMPH
+echo "#ifndef FFMPEG_CONFIG_H" >> $TMPH
+echo "#define FFMPEG_CONFIG_H" >> $TMPH
 echo "#define FFMPEG_CONFIGURATION \"$FFMPEG_CONFIGURATION\"" >> $TMPH
 
 echo "PREFIX=$PREFIX" >> config.mak
@@ -1942,6 +1944,8 @@ enabled asmalign_pot &&
   printf '#define ASMALIGN(ZEROBITS) ".align 1<<" #ZEROBITS "\\n\\t"\n' >> $TMPH
 
 
+echo "#endif /* FFMPEG_CONFIG_H */" >> $TMPH
+
 # Do not overwrite config.h if unchanged to avoid superfluous rebuilds.
 cmp -s $TMPH config.h &&
     echo "config.h is unchanged" ||