(posix_fileno) [_WIN32]: Rename posix_fileno() to fileno().

Remove the extern posix_fileno().

(fileno) [_WIN32]: Replace system fileno() with a function that supports posix
file descriptors.  Move #undef fileno to w32misc.h as the system define
is in stdio.h.

(rea) [_WIN32]: Add stdio.h for fileno() extern declaration and add misc.h
to ensure the WIN32 fixes to stdio.h are included.

src/lib/w32/posixio.c

@@ -129,7 +129,7 @@ set_fd(int fd, enum fdmap_io_type type, int handle)
     fdmap[fd].type = type;
 
     /*
-     * Garbage collection for posix_fileno(), currently not
+     * Garbage collection for fileno(), currently not
      * replacing fclose() and fcloseall() so do not know when
      * a stream is closed.
      */
@@ -586,7 +586,7 @@ writev(int fd, const struct iovec *iov, int iovcnt)
  * handle is reused.
  */
 int
-posix_fileno(FILE *stream)
+fileno(FILE *stream)
 {
     int fd;
     int handle;