avoid exporting a sleep() symbol from libcrypto

Since it seems only MSVC lacks sleep(), and it's only used by apps, lets
special-case that and make it available as a static inline function
instead.

crypto/compat/posix_win.c

@@ -242,10 +242,4 @@ int gettimeofday(struct timeval * tp, struct timezone * tzp)
 	return 0;
 }
 
-unsigned int sleep(unsigned int seconds)
-{
-	Sleep(seconds * 1000);
-	return seconds;
-}
-
 #endif