unix: Get minimal version compiling again.

unix/mpconfigport_minimal.h

@@ -40,6 +40,7 @@
 #define MICROPY_COMP_CONST          (0)
 #define MICROPY_MEM_STATS           (0)
 #define MICROPY_DEBUG_PRINTERS      (0)
+#define MICROPY_READER_POSIX        (1)
 #define MICROPY_HELPER_REPL         (1)
 #define MICROPY_HELPER_LEXER_UNIX   (1)
 #define MICROPY_ENABLE_SOURCE_LINE  (0)