[C++] function modifier like [[nodiscard]] and [[noreturn]] break highlighting

[Sainan]

// Good
const void* f() final;
// Bad
[[nodiscard]] const void* f() final;
[[noreturn]] const void* f() final;

[Sainan]

Might be related to #1408 although that's about "find symbol", but I suspect the root cause is the same.

[deathaxe]

C family hasn't been updated for a while, thus doesn't support most of the more modern language features right now.