MSVC: Enable building ocspcheck.

- Add `STDIN_FILENO` to compat unistd header.
- Use quotes to include compat getopt header in the compat unistd.
- Export additional symbols needed by ocspcheck (optarg, optind,
  ftruncate)

include/compat/unistd.h

@@ -23,6 +23,7 @@ ssize_t pwrite(int d, const void *buf, size_t nbytes, off_t offset);
 #include <io.h>
 #include <process.h>
 
+#define STDIN_FILENO    0
 #define STDOUT_FILENO   1
 #define STDERR_FILENO   2
 
@@ -65,7 +66,7 @@ int getentropy(void *buf, size_t buflen);
 #endif
 
 #ifndef HAVE_GETOPT
-#include <getopt.h>
+#include "getopt.h"
 #endif
 
 #ifndef HAVE_GETPAGESIZE