* ZJIT: Share more code with YJIT in jit.c

* Fix ZJIT references to JIT

With a well-timed OOM around a page switch in the backend, it can return
RetryOnNextPage twice and crash due to the assert. (More places can
signal OOM now since VirtualMem tracks Rust malloc heap size for
--yjit-mem-size.)

Return error in these cases instead of crashing.

Fixes: https://github.com/Shopify/ruby/issues/566

* YJIT: Local variable register allocation

* locals are not stack temps

* Rename RegTemps to RegMappings

* Rename RegMapping to RegOpnd

* Rename local_size to num_locals

* s/stack value/operand/

* Rename spill_temps() to spill_regs()

* Clarify when num_locals becomes None

* Mention that InsnOut uses different registers

* Rename get_reg_mapping to get_reg_opnd

* Resurrect --yjit-temp-regs capability

* Use MAX_CTX_TEMPS and MAX_CTX_LOCALS

This change implements a fallback mode for the `--yjit-dump-disasm`
development command-line option to make it usable in release builds.
Previously, using the option with release builds of YJIT yielded only
a warning asking the user to build with `--enable-yjit=dev`.

While builds that use the `disasm` feature still give the best output,
just having the comments is useful enough for many kinds of debugging.
Having it usable in release builds is nice for new hackers, too, since
this allows for tinkering without having to learn how to build YJIT in
development mode.

Sample output on A64:

```
  # regenerate_branch
  # Insn: 0001 opt_send_without_block (stack_size: 1)
  # guard known object with singleton class
  0x11f7e0034: 4b 00 00 58 03 00 00 14 08 ce 9c 04 01 00 00
  0x11f7e0043: 00 3f 00 0b eb 81 06 01 54 1f 20 03 d5
  # RUBY_VM_CHECK_INTS(ec)
  0x11f7e0050: 8b 02 42 b8 cb 07 01 35
  # stack overflow check
  0x11f7e0058: ab 62 02 91 7f 02 0b eb 69 07 01 54
  # save PC to CFP
  0x11f7e0064: 0b 3b 9a d2 2b 2f a0 f2 0b 00 cc f2 6b 02 00
  0x11f7e0073: f8 ab 82 00 91
```

To ensure this feature doesn't incur too much cost when running without
the `--yjit-dump-disasm` option, I checked that there is no significant
impact to compile time and memory usage with the `compile_time_ns` and
`yjit_alloc_size` entry in `RubyVM::YJIT.runtime_stats`. For each
sample, I ran 3 iterations of the `lobsters` YJIT benchmark. The
statistics summary and done with the `summary` function in R.

Compile time, sample size of 60, lower is better:

```
       Before              After
 Min.   :2.054e+09   Min.   :2.028e+09
 1st Qu.:2.069e+09   1st Qu.:2.044e+09
 Median :2.081e+09   Median :2.060e+09
 Mean   :2.089e+09   Mean   :2.066e+09
 3rd Qu.:2.109e+09   3rd Qu.:2.085e+09
 Max.   :2.146e+09   Max.   :2.144e+09
```

Allocation size, sample size of 20, lower is better:

```
       Before             After
 Min.   :21804742   Min.   :21794082
 1st Qu.:21826682   1st Qu.:21816282
 Median :21844042   Median :21826814
 Mean   :21960664   Mean   :22026291
 3rd Qu.:21861228   3rd Qu.:22040439
 Max.   :22587426   Max.   :22930614
```

The `yjit_alloc_size` samples are noisy, but since the average increased
by only 0.3%, and the median is lower, I feel safe saying that there is
no significant change.

* YJIT: A64: Add CBZ and CBNZ encoding functions

* YJIT: A64: Use CBZ/CBNZ to check for zero

Instead of emitting `cmp x0, #0` plus `b.z #target`, A64 offers Compare
and Branch on Zero for us to just do `cbz x0, #target`. This commit
utilizes that and the related CBNZ instruction when appropriate.

We check for zero most commonly in interrupt checks:

```diff
  # Insn: 0003 leave (stack_size: 1)
  # RUBY_VM_CHECK_INTS(ec)
  ldur w11, [x20, #0x20]
  -tst w11, w11
  -b.ne #0x109002164
  +cbnz w11, #0x1049021d0
```

* fix copy paste error

Co-authored-by: Randy Stauner <randy@r4s6.net>

---------

Co-authored-by: Randy Stauner <randy@r4s6.net>

Same idea as the x64 equivalent in c2622b52536c5, removing the register
shuffle coming from the pop two, push one stack motion these VM
instructions perform.

```
  # Insn: 0004 opt_or (stack_size: 2)
  - orr x11, x1, x9
  - mov x1, x11
  + orr x1, x1, x9
```

* YJIT: A64: Use ADDS/SUBS/CMP (immediate) when possible

We were loading 1 into a register and then doing ADDS/SUBS previously.
That was particularly bad since those come up in fixnum operations.

```diff
   # integer left shift with rhs=1
-  mov x11, #1
-  subs x11, x1, x11
+  subs x11, x1, #1
   lsl x12, x11, #1
   asr x13, x12, #1
   cmp x13, x11
-  b.ne #0x106ab60f8
-  mov x11, #1
-  adds x12, x12, x11
+  b.ne #0x10903a0f8
+  adds x12, x12, #1
   mov x1, x12
```

Note that it's fine to cast between i64 and u64 since the bit pattern is
preserved, and the add/sub themselves don't care about the signedness of
the operands.

CMP is just another mnemonic for SUBS.

* YJIT: A64: Split asm.mul() with immediates properly

There is in fact no MUL on A64 that takes an immediate, so this
instruction was using the wrong split method. No current usages of this
form in YJIT.

---------

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

I ran into this while trying to implement setbyte, was surprised
to find out we hadn't implemented it yet.