windows: Enable READER_POSIX to get access to lexer_new_from_file.

windows/mpconfigport.h

@@ -43,6 +43,7 @@
 #define MICROPY_MALLOC_USES_ALLOCATED_SIZE (1)
 #define MICROPY_MEM_STATS           (1)
 #define MICROPY_DEBUG_PRINTERS      (1)
+#define MICROPY_READER_POSIX        (1)
 #define MICROPY_USE_READLINE_HISTORY (1)
 #define MICROPY_HELPER_REPL         (1)
 #define MICROPY_REPL_EMACS_KEYS     (1)