Add an explicit "is_ghost" property to selected instructions, and use
that to determine whether reload and coloring should visit instructions.
This allows them to visit fallthrough_return instructions and insert
fills and register moves as needed.
* Rename size to base_size and introduce a compute_size function;
* Add infra to inspect in/outs registers when computing the size of an instruction;
* Remove the GPR_SAFE_DEREF and GPR_ZERO_DEREF_SAFE register classes on x86 (fixes#335);
* Add 'jump_table_entry' and 'indirect_jump' instructions.
* Update CodeSink to keep track of code size. Pretty up clif-util's disassembly output.
* Only disassemble the machine portion of output. Pretty print the read-only data after it.
* Update switch frontend code to use new br_table instruction w/ default.
