Tests: Add sample XCOFF binaries

Generate the binaries as follows:

    $ cat main.c
    int main(void) { return 0; }
    $ xlc -q64 -o xcoff64.bin -Wl,-blibpath:/sample/rpath:/usr/lib:/lib main.c
    $ strip -X 64 xcoff64.bin
    $ xlc -q32 -o xcoff32.bin -Wl,-blibpath:/sample/rpath:/usr/lib:/lib main.c
    $ strip -X 32 xcoff32.bin