Use a special breakpoint address if one isn't explicitly supplied in order to support natural line stepping.

ARM64 will not increment the program counter (PC) upon hitting a breakpoint instruction. Consequently, stepping through code with a debugger ends up looping back to the breakpoint instruction. LLDB has a special breakpoint address of 0xf000 that will increment the PC and allow the debugger to work as expected. This change makes it possible to debug YJIT generated code on ARM64.

More details at: https://discourse.llvm.org/t/stepping-over-a-brk-instruction-on-arm64/69766/8

Co-authored-by: Aaron Patterson <tenderlove@ruby-lang.org>

Mostly putting angle brackets around links to follow markdown syntax.

* 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>

* 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>

* YJIT: implement fast path for integer multiplication in opt_mult

* Update yjit/src/codegen.rs

Co-authored-by: Alan Wu <XrXr@users.noreply.github.com>

* Implement mul with overflow checking on arm64

* Fix missing semicolon

* Add arm splitting for lshift, rshift, urshift

---------

Co-authored-by: Alan Wu <XrXr@users.noreply.github.com>