* Recommend LSP's in development docs
Per conversation in #3338.
There are already a lot of documented compile options so I think we're
better off suggesting that everybody create a compile_commands.json
whether or not they're using an LSP because it doesn't cost much.
While I was at it it seemed reasonable to mention rust LSP too. Now that
rls is deprecated I'm not sure there is any competitor to rust-analyzer
worth mentioning.
* Export compile commands by default.
Thanks to @felixschurk for the idea and telling me how to do it.
It took me a minute to figure out that this places the
compile_commands.json in the build directory rather than the root of the
project. But clangd still finds it there and that's a better place for
it anyway.
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