This commit fixes a compile/link issue caused by vader. The vader btl
was using OPAL_THREAD_ADD64 to increment a counter which may not be
available on 32-bit systems. Changed to use OPAL_THREAD_ADD_SIZE_T
which will be 64-bit or 32-bit depending on the system.
Signed-off-by: Nathan Hjelm <hjelmn@lanl.gov>