Use read/write locking on Windows

Fixes #13914

The "SRWLock" synchronization primitive is available in Windows Vista
and later.  CRYPTO_THREAD functions now use SRWLock functions when the
target operating system supports them.

Reviewed-by: Paul Dale <pauli@openssl.org>
Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/14381)