Renaming uJIT to YJIT. AKA s/ujit/yjit/g.

Filter out counters that are zero and make it easier to have multiple
printout groups.

On `railsbench`:

```
opt_send_without_block exit reasons:
    se_finish_frame     184809 (100.0%)
```

These account for about 12% of the time when we were bailing from calls
in railsbench. `ratio_in_ujit` went up 0.1% with this change.

This allows counting things in generated code such as side exits or
different reasons for failing to compile. Runtime counters are exposed
to Ruby as `UJIT.runtime_stats` for ease of reporting and analysis.

* ujit: implement opt_getinlinecache

Aggressively bet that writes to constants don't happen and invalidate
all opt_getinlinecache blocks on any and all constant writes.

Use alignment padding on block_t to track this assumption. No change to
sizeof(block_t).

* Fix compile warnings when not RUBY_DEBUG
* Fix reversed condition
* Switch to st_table to keep track of assumptions

Co-authored-by: Aaron Patterson <aaron.patterson@gmail.com>
Co-authored-by: Maxime Chevalier-Boisvert <maximechevalierb@gmail.com>

* Tie lifetime of uJIT blocks to iseqs

   Blocks weren't being freed when iseqs are collected.

* Add rb_dary. Use it for method dependency table

* Keep track of blocks per iseq

  Remove global version_tbl

* Block version bookkeeping fix

* dary -> darray

* free ujit_blocks

* comment about size of ujit_blocks

shopify/ruby#29

Co-authored-by: Maxime Chevalier-Boisvert <maxime.chevalierboisvert@shopify.com>

VM and ujit instruction counting in debug builds.

shopify/ruby#19