Add: opend-xpack-emscripten Support

[kassane]

More info:

• D GC for WebAssembly #40

---

• test druntime features (dynArray, array append, class, string-literal concat)
• test std (phobos2) features
• adapt or make new example(s)

NOT MERGE

[adamdruppe]

Having the hash in there is kinda annoying since every time I push up a new opend version it is going to change. I don't want to keep old versions around though, that's a support burden id rather avoid - my policy you either have the newest, or you have an unsupported old thing you should update.

[kassane]

Having the hash in there is kinda annoying since every time I push up a new opend version it is going to change.

Yeah! Continuously changing the tarball hash is complicated since openD currently only has master/nightly.

I intend to fix this by replacing the use of Zon for xpack-emscripten and using zig fetch (replacing curl/git clone) without involving any extra dependencies.

• zig fetch without Zon - by John Marler

[kassane]

I intend to fix this by replacing the use of Zon for xpack-emscripten and using zig fetch (replacing curl/git clone) without involving any extra dependencies.

It's need run zig fetch to always get the latest hash file.

$ zig fetch --debug-hash https://github.com/opendlang/opend/releases/download/CI/opend-latest-xpack-emscripten.tar.xz
file: de5f0d6a92ff12c9ea0574cafdec166a58c0ff38a0ca806dcd847ff54580ea76: lib/libdruntime-ldc-debug.a
file: 67b56e633547fc304adb05af21df59521b10984742c096909dcd131aaddc64c7: lib/libdruntime-ldc.a
file: 977c4023e7c01c5c39500ef43c931aa2b43c09f7437f5e479f9699117fff5659: lib/libphobos2-ldc-debug.a
file: e9ae86c4c456735782722b24d795640e785791e45c4525e0ab33bbd48bc0d21d: lib/libphobos2-ldc.a
1220d360d5eea58135fc6aa9f69036c4683e74b428a3a55235229b5bb60b805a68f1 #hash path ($HOME/.cache/zig/p/{hash})

# hash path only
zig fetch https://github.com/opendlang/opend/releases/download/CI/opend-latest-xpack-emscripten.tar.xz 
1220d360d5eea58135fc6aa9f69036c4683e74b428a3a55235229b5bb60b805a68f1

[kassane]

commit: de6b271 - optional verify checksums

Ref. Tigerbeetle
https://github.com/tigerbeetle/tigerbeetle/blob/274de35df357b790f0ccddded3531bb2592fbe2f/build.zig#L1683-L1738