[MWF] Fix finding of X11 shared library on Ubuntu (#708856)

When libX11-dev is not installed on an end-user's machine MWF apps
will crash in XCreateFontSet. This change uses dynamic search path
when building instead of hard coded directories when
searching for libX11.so.*. This fixes bug 708856
(https://bugzilla.novell.com/show_bug.cgi?id=708856).