threads_win: fix build error with VS2010

VC 2010 or earlier compilers do not support static inline.
To work around this problem, we can use the ossl_inline macro.

Fixes:
crypto\threads_win.c(171) : error C2054: expected '(' to follow 'inline'
crypto\threads_win.c(172) : error C2085: 'get_hold_current_qp' : not in formal parameter list
crypto\threads_win.c(172) : error C2143: syntax error : missing ';' before '{'
crypto\threads_win.c(228) : warning C4013: 'get_hold_current_qp' undefined; assuming extern returning int
crypto\threads_win.c(228) : warning C4047: '=' : 'rcu_qp *' differs in levels of indirection from 'int'

Signed-off-by: Georgi Valkov <gvalkov@gmail.com>

crypto/threads_win.c

@@ -168,7 +168,7 @@ void ossl_rcu_lock_free(CRYPTO_RCU_LOCK *lock)
     OPENSSL_free(lock);
 }
 
-static inline struct rcu_qp *get_hold_current_qp(CRYPTO_RCU_LOCK *lock)
+static ossl_inline struct rcu_qp *get_hold_current_qp(CRYPTO_RCU_LOCK *lock)
 {
     uint32_t qp_idx;