Clang-upc 32 bit implementation - first try.
Check for 32/64 bit target for proper struct pointer rep.
Remove setting of bit sizes for struct pointer representation and only
make sure that preprocessor has correct defines for them.  At the point
of compiler invocation we do not know the target bit size (32 v. 64).
Fix the test for 32-bit shared PTS.
Merge changes for 32-bit Clang UPC port.