This adds support for binary generation for the new EH proposal.
So far the only case that we emitted variable immediate operands in
binary has been `br_table`'s destinations. (Other `variable_ops` uses in
TableGen files are register operands, such as the operands of `call`, so
they don't get emitted in binary as a part of the same instruction.)
With this PR, variable immediate operands can include `try_table`'s
operands:
- The number of of catch clauses
- catch clauses sub-opcodes
- `catch`: 0x00
- `catch_ref`: 0x01
- `catch_all`: 0x02
- `catch_all_ref`: 0x03
- catch clauses' destinations
With `try_table`, we now have variable expr operands for `try_table`'s
catch clauses' tags. We treat their fixups in the same way we do for
tags in other instructions such as in `throw`.
Diff without whitespace will be easier to view.
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