Pacify file locks on Windows

This change gets redbean SQLite working in write mode on Windows.
Warnings have been added to the appropriate and responsible places.
Hacking proprietary PC systems into production-worthy servers isn't
terribly high on the list of priorities. Consider BSD or Linux when
building online systems that service requests from multiple people.

Fixes #193

libc/calls/fcntl.c

@@ -31,6 +31,9 @@
  *     // ...
  *     CHECK_NE(-1, fcntl(zfd, F_SETLK, &(struct flock){F_UNLCK}));
  *
+ * Please be warned that locks currently do nothing on Windows since
+ * figuring out how to polyfill them correctly is a work in progress.
+ *
  * @param cmd can be F_{GET,SET}{FD,FL}, etc.
  * @param arg can be FD_CLOEXEC, etc. depending
  * @return 0 on success, or -1 w/ errno