MSVC: compat: disable pthread_mutex_timedlock on Windows

On Windows there's no gettimeofday()/nanosleep(), and the usual
suggestions come with a big disclaimer saying that it is not intended
for high-resolution timing. Since this is not needed by the initial port
of libyang to MSVC, let's just comment this out.
diff --git a/compat/compat.c b/compat/compat.c
index fe50092..ea8eb03 100644
--- a/compat/compat.c
+++ b/compat/compat.c
@@ -202,6 +202,7 @@
 
 #endif
 
+#ifndef _MSC_VER
 #ifndef HAVE_PTHREAD_MUTEX_TIMEDLOCK
 int
 pthread_mutex_timedlock(pthread_mutex_t *mutex, const struct timespec *abstime)
@@ -250,6 +251,7 @@
 }
 
 #endif
+#endif
 
 #ifndef HAVE_REALPATH
 #ifdef _WIN32