iseq.h (struct iseq_catch_table_entry): shrink to 32 bytes on 64-bit

* iseq.h (struct iseq_catch_table_entry): shrink to 32 bytes on 64-bit

This drops a few minor page faults on my system at startup.
Using 64-bit start, end, cont, and sp fields are unnecessary as
label_get_position and label_get_sp only return int values.
label_get_position and label_get_sp should probably return
unsigned, but that is a future change.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@46813 b2dd03c8-39d4-4d8f-98ff-823fe69b080e