compat: there's no <sys/time.h> on MSVC

...but we won't be really using gettimeofday() there because
pthread_mutex_timedlock is provided by the pthread compatibility library
that we depend on.
diff --git a/compat/compat.c b/compat/compat.c
index bf75c74..d75b961 100644
--- a/compat/compat.c
+++ b/compat/compat.c
@@ -24,7 +24,9 @@
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
+#ifndef _MSC_VER
 #include <sys/time.h>
+#endif
 #include <time.h>
 #include <unistd.h>