CI: add WASM job

[Bodigrim]

Draft, just to get feedback from GHA.

[Bodigrim]

@amesgen @TerrorJack any clues what's up with WASM CI job here?

    IO
      readFile.writeFile:                                  OK (0.04s)
        +++ OK, passed 100 tests.
      readFile.writeFile:                                  OK (0.04s)
        +++ OK, passed 100 tests.
      readFile.writeFile:                                  OK (0.04s)
        +++ OK, passed 100 tests.
      readFile.writeFile:                                  OK (0.04s)
        +++ OK, passed 100 tests.
      appendFile        :                                  FAIL
        *** Failed! Falsified (after 5 tests and 4 shrinks):
        "\NUL"
        "\NUL"
        "\NUL" /= "\NUL\NUL"
        Use --quickcheck-replay=901105 to reproduce.
        Use -p '$0=="All.Properties.IO.appendFile        "' to rerun this test only.
      appendFile        :                                  FAIL
        *** Failed! Falsified (after 5 tests and 3 shrinks):
        "\NUL"
        "\NUL"
        "\NUL" /= "\NUL\NUL"
        Use --quickcheck-replay=109253 to reproduce.
        Use -p '$0=="All.Properties.IO.appendFile        "' to rerun this test only.
      appendFile        :                                  FAIL
        *** Failed! Falsified (after 4 tests):
        "\SOH\SOH"
        "\STX"
        "\STX\SOH" /= "\SOH\SOH\STX"
        Use --quickcheck-replay=958508 to reproduce.
        Use -p '$0=="All.Properties.IO.appendFile        "' to rerun this test only.
      appendFile        :                                  FAIL
        *** Failed! Falsified (after 5 tests):
        "\NUL"
        "\STX"
        "\STX" /= "\NUL\STX"
        Use --quickcheck-replay=699923 to reproduce.
        Use -p '$0=="All.Properties.IO.appendFile        "' to rerun this test only.

writeFile . readFile passes, but if there is appendFile in between, it fails.

[TerrorJack]

openFile with AppendMode in wasm backend is only recently fixed by https://gitlab.haskell.org/ghc/ghc/-/merge_requests/11697 (see openFile009 test case), though ghc-wasm-meta's master branch has been stalled for a while because of a wasi-sdk bump that hasn't landed in 9.6/9.8 branches yet...

Maybe try using ghcup to set it up, my impression is it pulls in more recent metadata.

[clyring]

I've seen something just like this Windows/9.8 failure before, in CI for the bytestring-0.11 branch at 834bbe4. It was "fixed" when I bumped the version in bytestring.cabal to one that differed from the relevant ghc boot library version.

[clyring]

I'm not sure I'm fully competent to review this, but it looks very plausible and seems to be working as expected.