add .clangd

[henrij22]

This enhances the clangd langauge server.

Add: -include=build/config.h

• Now preprocessor directives declared in config.h are processed

Remove: -fext-numeric-literals

• fixes a clangd issue where a error would always appear at the top of the file regarding unknown arguments (see screenshot)

  (see also https://stackoverflow.com/questions/39178288/why-dont-complex-number-literals-work-in-clang)

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 91.62%. Comparing base (64a6b3a) to head (f9894a9). Report is 1 commits behind head on main.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #313 +/- ## ======================================= Coverage 91.62% 91.62% ======================================= Files 66 66 Lines 2327 2327 ======================================= Hits 2132 2132 Misses 195 195 ``` | [Flag](https://app.codecov.io/gh/ikarus-project/ikarus/pull/313/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=ikarus-project) | Coverage Δ | | |---|---|---| | [tests](https://app.codecov.io/gh/ikarus-project/ikarus/pull/313/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=ikarus-project) | `91.62% <ø> (ø)` | | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=ikarus-project#carryforward-flags-in-the-pull-request-comment) to find out more.

:umbrella: View full report in Codecov by Sentry.
:loudspeaker: Have feedback on the report? Share it here.

[rath3t]

Are there other nice option we want to include there?

[henrij22]

Not sure yet, in the future we might want to define a set of clang-tidy options that we want to enforce and add this to this file.

See also https://clangd.llvm.org/config