[llvm] [CMake] Fix config when static zstd libraries are not found (PR #113584)

[Aaron Puchert via llvm-commits]

================
@@ -196,7 +196,18 @@ if(LLVM_ENABLE_ZSTD)
     find_package(zstd QUIET)
   endif()
 endif()
----------------
aaronpuchert wrote:

But I don't see why this is not in this `if`. We should probably not care about `LLVM_USE_STATIC_ZSTD` if `LLVM_ENABLE_ZSTD` is off. As for the `LLVM_USE_SANITIZER MATCHES "Memory.*"` case, I guess that is acceptable.

https://github.com/llvm/llvm-project/pull/113584