OPENSSL_USE_STATIC_LIBS has no impact when building with LLVM on Windows platform
OPENSSL_USE_STATIC_LIBS should statically link openssl libraries, however, when llvm is used on Windows it will keep dynamically linking OpenSSL-Win32/lib/librycpto.lib. When MSVC is used, openssl will be statically linked.
https://cmake.org/cmake/help/latest/module/FindOpenSSL.html does not mention that MSVC has to be used if openssl is to be linked statically.