Remove unused -XCPP

[philderbeast]

Fixes #10720, a follow on from #10092. Removes unused {-# LANGUAGE CPP #-} pragmas.

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Template B: This PR does not modify behaviour or interface

• Patches conform to the coding conventions.
• Is this a PR that fixes CI? If so, it will need to be backported to older cabal release branches (ask maintainers for directions).

Manual QA Notes

Please delete dist-newstyle and run the following to check for occurrences of unused -XCPP:

$ grep '^#if' --files-without-match $(grep -R --files-with-matches 'LANGUAGE.*CPP' */**/*.hs)
cabal-testsuite/PackageTests/Backpack/bkpcabal01/p/P.hs
cabal-testsuite/PackageTests/CabalMacros/Mdl.hs
cabal-testsuite/PackageTests/CmmSources/src/Demo.hs
cabal-testsuite/PackageTests/CmmSourcesDyn/demo/Main.hs
cabal-testsuite/PackageTests/CmmSourcesDyn/src/Demo.hs
cabal-testsuite/PackageTests/CmmSourcesExe/src/Demo.hs
cabal-testsuite/PackageTests/Haddock/CPP.hs
cabal-testsuite/PackageTests/PreProcess/Hsc2HsOptionsCC/Main.hs
cabal-testsuite/PackageTests/Regression/T5386/Foo.hs
Cabal/src/Distribution/Simple/Build/PathsModule/Z.hs

$ grep 'LANGUAGE CPP' Cabal/src/Distribution/Simple/Build/PathsModule/Z.hs
    tell "{-# LANGUAGE CPP #-}\n"

Those in cabal-testsuite/PackageTests are part of tests so should likely stay put and Distribution.Simple.Build.PathsModule.Z is generating a paths module using a zinza template. It's a false positive find with the unrefined grep pattern, LANGUAGE.*CPP.

[ulysses4ever]

I think the commits should be squashed before merging.

[philderbeast]

I think the commits should be squashed before merging.

Yeah I can do that.

As it stands this pull request has 66 files split into 7 commits, one per package.

We don't release every package at once any more and there's backports that I haven't been involved in. I'm being cautious here. Squashing won't make later maintenance harder, will it?

@Mikolaj and @Kleidukos with changes like this that touch many files, do we have to be careful about consequences outside merging to the master branch?

[Mikolaj]

I guess squashing may make merging a tiny bit harder in this particular case, but not by much. Generally, I don't think there's any way to minimize conflicts from this PR, so let's just merge it and let others resolve them.

[Mikolaj]

Thank you.

[philderbeast]

so let's just merge it and let others resolve them

Thanks for the approval @Mikolaj. I read that as let's just merge it (squashed) which is what I'll do.