Document the need for the DTrace package SUNWdtrd on Solaris 8/9

The hotspot builds require access to a DTrace compiler (not the DTrace runtime support) on the Solaris system doing the build. This means that sparc, sparcv9, and i586 Solaris build machines need this formal SUNW package installed on them if you want a valid build of Mustang. (Solaris amd64 builds are done on Solaris 10 so don't need this package, and any sparc, sparcv9, or i586 bbuilds done on Solaris 10 or newer won't need the package either).

The DTrace *.d files are run through the DTrace compiler to generate *.o files that get added into the list of *.o files that create the Solaris shared library (*.so) or Solaris executables.