[Beaglebone] libXext.a: Not a valid libtool archive


currently I am trying to compile openbox-3.5.0 for my beaglebone.
Unfortunately the installed libXext (via opkg) isn't a shared
library...and libtool says

    /bin/sh ./libtool --silent --tag=CC --mode=link gcc -DNDEBUG
    -DG_DISABLE_ASSERT -fno-strict-aliasing -version-info 0:1:0 -o
    obt/libobt.la -rpath /usr/local/lib obt/obt_libobt_la-display.lo
    obt/obt_libobt_la-keyboard.lo obt/obt_libobt_la-xml.lo
    obt/obt_libobt_la-ddparse.lo obt/obt_libobt_la-link.lo
    obt/obt_libobt_la-paths.lo obt/obt_libobt_la-prop.lo
    obt/obt_libobt_la-signal.lo obt/obt_libobt_la-xqueue.lo -lXext
    -lXrender -lXrandr -lXext -lXext -lglib-2.0 -lxml2 sed:
    =/usr/lib/libXext.la: No such file or directory libtool: link:
    `=/usr/lib/libXext.la' is not a valid libtool archive make[1]: ***
    [obt/libobt.la] Error 1 make[1]: Leaving directory
    `/home/root/NFS/op2/openbox-3.5.0' make: *** [all-recursive] Error

Is there a way to get the libXext as an shared library or too
circumvent the problem?

Thank you very much in advance for any help!
Best regards,