Specify default exe extension on wasm32 to be .wasm

[TerrorJack]

This PR changes default exe extension on wasm32 to be .wasm, following convention of other WebAssembly toolchains. This is a part of the effort tracked in https://gitlab.haskell.org/ghc/ghc/-/issues/22594.

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Please include the following checklist in your PR:

• Patches conform to the coding conventions.
• Any changes that could be relevant to users have been recorded in the changelog.
• The documentation has been updated, if necessary.

[ulysses4ever]

@TerrorJack thanks for the patch and congrats with getting the necessary approvals! The procedure now is that you apply one of the two merge-me labels to hand it over to the bot.

In my opinion, this patch could be improved with a test. But I don't want to hold it hostage to a test.

[TerrorJack]

@ulysses4ever Thanks for the reminder!

Re label: it seems I'm not a contributor to this repo, so I don't see the option to edit labels on this PR. If I can be granted contributor right or someone adds a merge-me label here, that'll be appreciated :)

Re test: another MR in GHC (!9533) needs to land, and then it may be possible to test it meaningfully.

[ulysses4ever]

Ah, good to know!

@Mikolaj will see to the label/permissions business, I hope

[ulysses4ever]

In the meantime, I added the merge-me label.

[Mikolaj]

@TerrorJack: please kindly receive the Triage authority for our humble repo.

[TerrorJack]

The honor is mine :)

[jneira]

This could have a test? It seems to me that Cabal integration with wasm should be tested somehow

[TerrorJack]

@jneira I can think of a simple E2E test that invokes Setup.hs for a cabal exe component. But that needs to install a separate ghc in CI that targets wasm, and IIUIC all current cabal tests only rely on a single host GHC?

By any chance I'd be happy to add such a test if the idea sounds good to you; I'm working on unblocking wasm CI for GHC 9.6 release and after that I can revisit this issue.

[jneira]

It sounds great. I guess some e2e test for wasm would be needed sooner or later and well, maybe this pr is not the best place.
I only would ask to create an issue about such test, linking the already merged prs.

Cabal tests in ci uses the default ghc, yeah, but i think there are guards to run tests conditionally on ghc version and these tests will need it.