Github actions: Simplify build

[Geod24]

I've recently experienced a little issue which exposed a discrepancy between g++ and clang build, due to the install step, so now trying to use it everywhere.

[dlang-bot]

Thanks for your pull request, @Geod24!

Bugzilla references

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If your PR contains non-trivial changes, please reference a Bugzilla issue or create a manual changelog.

Testing this PR locally

If you don't have a local development environment setup, you can use Digger to test this PR:

dub run digger -- build "master + dmd#14289"

[thewilsonator]

Error: don't know how to make '../dmd/druntime/lib/druntime64.lib'

[ibuclaw]

Error: don't know how to make '../dmd/druntime/lib/druntime64.lib'

Whoops! The default windows makefile targets only build the compiler.

[Geod24]

Whoops! The default windows makefile targets only build the compiler.

I thought so too, but actually invoking druntime/win*.mak led to infinite recursion. Will get to it soonish.