Add WASI support to compiler and DRuntime

[QuantumSegfault]

Adds WASI support for LDC and DRuntime.

Based on my various related PRs upstream.

Phobos, GC, and EH are not yet functional. Use manual GC or run GC.disable to prevent unexpected frees

[QuantumSegfault]

Not quite ready yet.

Still needs a few tweaks...

[QuantumSegfault]

Requesting review
@adamdruppe

[adamdruppe]

eyeballs fine... let's just merge and run lol

[QuantumSegfault]

Hmm....

bb.0 (%ir-block.0):
  liveins: $arguments
  RETURN %1:i32, implicit-def dead $arguments

# End machine code for function _D4core6thread8osthread11getStackTopFNbNiZPv.

*** Bad machine code: Reading virtual register without a def ***
- function:    _D4core6thread8osthread11getStackTopFNbNiZPv
- basic block: %bb.0  (0x56176c95ee00)
- instruction: RETURN %1:i32, implicit-def dead $arguments
- operand 0:   %1:i32
LLVM ERROR: Found 1 machine code errors.

Didn't do that on LLVM 19.

Let me open PR against LDC and see if LLVM 18 CI has the issue.

[adamdruppe]

yes indeed, that's the emscripten build in the ci so maybe that is a bit different too, but it would still trigger version webassembly etc.