1) I modified build_visit so that it builds ADIOS on a larger range of
   platforms. The user needs to set both the MPICC and MPICXX environment
   variables for it to build properly.

2) I modified the thembisa config site file to build visit with ADIOS.
   This resolves #1852.



git-svn-id: http://visit.ilight.com/svn/visit/trunk/src@23375 18c085ea-50e0-402c-830e-de6fd14e8384