[all-commits] [llvm/llvm-project] 55d5ba: [NFC] Fix compilation in C++20 mode with GCC 12

[Ilya Biryukov via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 55d5ba905da0db55282dd3985761ddf3dd452fd1
      https://github.com/llvm/llvm-project/commit/55d5ba905da0db55282dd3985761ddf3dd452fd1
  Author: Ilya Biryukov <ibiryukov at google.com>
  Date:   2024-01-03 (Wed, 03 Jan 2024)

  Changed paths:
    M clang/lib/Sema/SemaChecking.cpp

  Log Message:
  -----------
  [NFC] Fix compilation in C++20 mode with GCC 12

I ran into the following compiler error when trying to build with GCC 12
and `-DCMAKE_CXX_STANDARD=20`:
```
llvm-project/clang/lib/Sema/SemaChecking.cpp:16690:16:   required from here
/usr/include/c++/12/type_traits:971:30: error: default member initializer for '{anonymous}::SequenceChecker::Usage::UsageExpr' required before the end of its enclosing class
```

The error seems correct, GCC just instantiates the `SmallDenseMap`
early and detects it. Clang does not, but that's an acceptable
implementation difference as far as the standard is concerned.

Move constructor outside the class to avoid this problem.