vm_core.h (struct rb_iseq_struct): reduce to 296 bytes on 64-bit

Most iseq do not have a catch_table, so avoid needlessly adding
4-8 bytes to the struct for the common case.

Changes from v2:
- iseq_catch_table_size removed, use if (...) for (;...;)

Changes from v1:
- renamed iseq->_catch_table to iseq->catch_table
- iseq_catch_table_bytes: made a static inline function
- iseq_catch_table_size: new function replaces the
  iseq_catch_table_each iterator macro

* iseq.h (struct iseq_catch_table): new flexible array struct
         (iseq_catch_table_bytes): allocated size function
* vm_core.h (struct rb_iseq_struct): uupdate catch_table member
* compile.c (iseq_set_exception_table): update for struct changes
* iseq.c (iseq_free): ditto
* iseq.c (iseq_memsize): ditto
* iseq.c (rb_iseq_disasm): ditto
* iseq.c (iseq_data_to_ary): ditto
* iseq.c (rb_iseq_build_for_ruby2cext): ditto (untested)
* vm.c (vm_exec): ditto
* vm_core.h (struct rb_iseq_struct): ditto
* vm_insnhelper.c (vm_throw): ditto

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@46811 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
* 2014-07-14

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@46812 b2dd03c8-39d4-4d8f-98ff-823fe69b080e