The objects in this prebuilt directory can be rebuilt from the source in
$ANDROID/external/qemu/distrib/sdl-1.2.12.

The current version was built from commit
    <562240d8235c122b1624713169cd0764d84956d2>
with the commands

For 32-bit
$ cd $ANDROID/external/qemu/distrib/sdl-1.2.12
$ ./android-configure.sh
$ make
$ make install
$ cp -a out/linux-x86/* $ANDROID/prebuilt/linux-x86/sdl

To add 64-bit *.a (after successful 32-bit build)
$ cd $ANDROID/external/qemu/distrib/sdl-1.2.12
$ ./android-configure.sh --try-64
$ make
$ cp objs/libs/libSDL.a $ANDROID/prebuilt/linux-x86/sdl/libs/lib64SDL.a
$ cp objs/libs/libSDLmain.a $ANDROID/prebuilt/linux-x86/sdl/libs/lib64SDLmain.a