Revert "Redefine semantics of lsda for pr0,1,2 functions. Not sure this is right but it seems more consistent"

This reverts commit c2692319e4a049fd97e9d109f0312c7827d4215f.
Attempt to implement basic descriptor parsing and type mathcing

Change-Id: I3a26e5947a2778d9598cf58abe45d83e00b7af5c