crypto/rand/rand_win.c: include "e_os.h" to get the default _WIN32_WINNT

This helps decide if the BCrypt API should be used or not.

Fixes #8635

Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/8638)

(cherry picked from commit cc8926ec)