Use [[likely]] and [[unlikely]] in c++20 mode

[elshize]

When compiling in the c++20 mode, use the standard [[likely]] and [[unlikely]] instead of GNU built-ins. It enables these directives on other platforms.

All uses of our macros had to be edited to remove the outer parentheses.

Implements: https://github.com/pisa-engine/pisa/issues/570

[codecov[bot]]

Codecov Report

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

Comparison is base (aa8900b) 93.28% compared to head (e4963e9) 93.28%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #576 +/- ## ======================================= Coverage 93.28% 93.28% ======================================= Files 90 90 Lines 4454 4454 ======================================= Hits 4155 4155 Misses 299 299 ```

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