CMake build enables all compiler warnings when building with clang-cl #2448

Describe the bug
When building zstd using clang-cl, the LLVM MSVC-compatible driver, zstd's CMake build emits a very large number of compiler warnings, because zstd's build incorrectly passes -Wall to the compiler. [Source]

For compatibility with MSVC, when -Wall is passed to clang-cl, it's translated to -Weverything.

Note that when using clang-cl, CMake sets CMAKE_C_COMPILER_ID to "Clang" and MSVC to TRUE.

To Reproduce
In a MSVC developer prompt with cmake, ninja and clang-cl available on PATH:

cmake \path\to\zstd\build\cmake -DCMAKE_C_COMPILER=clang-cl -DCMAKE_CXX_COMPILER=clang-cl -GNinja
cmake --build .

Expected behavior
A (mostly?) warning-free build.

Screenshots and charts
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Desktop (please complete the following information):

• OS: Windows 10
• Version [e.g. 22] 20H2
• Compiler MSVC 14.28 / LLVM 11.0.0
• Flags [e.g O2]
• Other relevant hardware specs [e.g. Dual-core]
• Build system: CMake 3.19.2

Additional context
Add any other context about the problem here.