Separated MSVC and clang-cl settings for Windows

[emmenlau]

This PR makes a minor improvement when building with LLVM clang-cl on Windows. One of the compile flags is not needed by clang-cl and should only be used with MSVC compilers.

• Did you create an Apache Jira ticket? (Request account here, not required for trivial changes)
• If a ticket exists: Does your pull request title follow the pattern "THRIFT-NNNN: describe my issue"?
• Did you squash your changes to a single commit? (not required, but preferred)
• Did you do your best to avoid breaking changes? If one was needed, did you label the Jira ticket with "Breaking-Change"?
• If your change does not involve any code, include [skip ci] anywhere in the commit message to free up build resources.