Provide mp_errno_to_str even without uerrno

We can provide a basic version of mp_errno_to_str even if the uerrno
module won't be provided.  Rather than looking errno names up in the
uerrno module's globals dict, we'll just rely on a simple mapping in the
function itself.

Author: godlygeek

py/moduerrno.c

@@ -30,8 +30,6 @@
 #include "py/obj.h"
 #include "py/mperrno.h"
 
-#if MICROPY_PY_UERRNO
-
 // This list can be defined per port in mpconfigport.h to tailor it to a
 // specific port's needs.  If it's not defined then we provide a default.
 #ifndef MICROPY_PY_UERRNO_LIST
@@ -61,6 +59,8 @@
 
 #endif
 
+#if MICROPY_PY_UERRNO
+
 #if MICROPY_PY_UERRNO_ERRORCODE
 STATIC const mp_rom_map_elem_t errorcode_table[] = {
     #define X(e) { MP_ROM_INT(MP_ ## e), MP_ROM_QSTR(MP_QSTR_## e) },
@@ -133,4 +133,15 @@ qstr mp_errno_to_str(mp_obj_t errno_val) {
     #endif
 }
 
+#else //MICROPY_PY_UERRNO
+
+qstr mp_errno_to_str(mp_obj_t errno_val) {
+    int v = MP_OBJ_SMALL_INT_VALUE(errno_val);
+    #define X(e) if (v == e) return (MP_QSTR_ ## e);
+    MICROPY_PY_UERRNO_LIST
+    #undef X
+
+    return MP_QSTR_;
+}
+
 #endif //MICROPY_PY_UERRNO

py/mperrno.h

@@ -142,12 +142,6 @@
 
 #endif
 
-#if MICROPY_PY_UERRNO
-
-#include "py/obj.h"
-
 qstr mp_errno_to_str(mp_obj_t errno_val);
 
-#endif
-
 #endif // MICROPY_INCLUDED_PY_MPERRNO_H

py/objexcept.c

@@ -113,7 +113,6 @@ STATIC void mp_obj_exception_print(const mp_print_t *print, mp_obj_t o_in, mp_pr
             mp_print_str(print, "");
             return;
         } else if (o->args->len == 1) {
-            #if MICROPY_PY_UERRNO
             // try to provide a nice OSError error message
             if (o->base.type == &mp_type_OSError && MP_OBJ_IS_SMALL_INT(o->args->items[0])) {
                 qstr qst = mp_errno_to_str(o->args->items[0]);
@@ -122,7 +121,6 @@ STATIC void mp_obj_exception_print(const mp_print_t *print, mp_obj_t o_in, mp_pr
                     return;
                 }
             }
-            #endif
             mp_obj_print_helper(print, o->args->items[0], PRINT_STR);
             return;
         }