Update SDL to 2.0.18

libs/SDL2/build-scripts/updaterev.sh

@@ -8,10 +8,9 @@ srcdir=..
 header=$outdir/include/SDL_revision.h
 
 rev=`sh showrev.sh 2>/dev/null`
-if [ "$rev" != "" -a "$rev" != "hg-0:baadf00d" ]; then
-    revnum=`echo $rev | sed 's,hg-\([0-9]*\).*,\1,'`
+if [ "$rev" != "" ]; then
     echo "#define SDL_REVISION \"$rev\"" >"$header.new"
-    echo "#define SDL_REVISION_NUMBER $revnum" >>"$header.new"
+    echo "#define SDL_REVISION_NUMBER 0" >>"$header.new"
     if diff $header $header.new >/dev/null 2>&1; then
         rm "$header.new"
     else