PSA: clang-cl /Wall does not mean clang -Wall. It means clang -Weverything.

clang-cl /W1, clang-cl /W2, and clang-cl /W3 all mean clang -Wall.

clang-cl /W4 means clang -Wall -Wextra.

If you're familiar with MSVC [1], this will not be surprising to you, but I was not!

[1]: https://learn.microsoft.com/en-us/cpp/build/reference/compiler-option-warning-level?view=msvc-170