compat: fix building clock_nanosleep function on OpenBSD

../compat/clock_nanosleep.c:46:9: error: use of undeclared identifier 'errno'
        errno = EINVAL;
        ^
../compat/clock_nanosleep.c:56:13: error: use of undeclared identifier 'errno'
            errno = EINVAL;
            ^
../compat/clock_nanosleep.c:94:9: error: use of undeclared identifier 'errno'
        errno = EINVAL;
        ^
3 errors generated.

compat/clock_nanosleep.c

@@ -28,7 +28,7 @@
 
 #include <assert.h>
 #include <pthread.h>
-#include <sys/errno.h>
+#include <errno.h>
 #include <sys/types.h>
 #include <sys/time.h>
 #include <sys/sysctl.h>