configure finds appropriate default 32-bit or 64-bit Dyninst libraries

configure finds appropriate default 32-bit or 64-bit Dyninst libraries

Earlier versions of the systemtap configuration would just include
two -L paths to both 32-bit and 64-bit versions of the Dyninst
libraries.  However, attempting to link a 32-bit library with a 64-bit
build (and vice versa) may cause the build to fail.  This revision of
the configure tests determines which default Dyninst library works
with the compiler being used and selects it.

The configure can't bindly use ${libdir}/dyninst to select the path to
the default Dyninst libary as this only selects the ${prefix}/lib64 on
appropriate machines if the prefix is /usr.  If the prefix is set to
something else, ${libdir} is always ${prefix}/lib.  The would cause
the build to attempt to link with nonexistent Dyninst libaries in the
${prefix} directory.  If systemtap needs to be use a version of
Dysninst in a non-standard place, the --with-dyninst=<path_to_dyninst>
should be used.