minimal: Make build more flexible and work as 64-bit build.

Changes are:
- string0 is no longer built when building for host as the target, because
  it'll be provided by the system libc and may in some cases clash with the
  system one (eg on OSX).
- mp_int_t/mp_uint_t are defined in terms of intptr_t/uintptr_t to support
  both 32-bit and 64-bit builds.
- Configuration values which are the default in py/mpconfig.h are removed
  from mpconfigport.h to make the configuration a bit more minimal, eg as
  a better starting point for new ports.

ports/minimal/Makefile

@@ -49,10 +49,13 @@ SRC_C = \
 	lib/utils/printf.c \
 	lib/utils/stdout_helpers.c \
 	lib/utils/pyexec.c \
-	lib/libc/string0.c \
 	lib/mp-readline/readline.c \
 	$(BUILD)/_frozen_mpy.c \
 
+ifeq ($(CROSS), 1)
+SRC_C += lib/libc/string0.c
+endif
+
 OBJ = $(PY_CORE_O) $(addprefix $(BUILD)/, $(SRC_C:.c=.o))
 
 ifeq ($(CROSS), 1)

ports/minimal/main.c

@@ -60,6 +60,7 @@ int main(int argc, char **argv) {
     return 0;
 }
 
+#if MICROPY_ENABLE_GC
 void gc_collect(void) {
     // WARNING: This gc_collect implementation doesn't try to get root
     // pointers from CPU registers, and thus may function incorrectly.
@@ -69,6 +70,7 @@ void gc_collect(void) {
     gc_collect_end();
     gc_dump_info();
 }
+#endif
 
 mp_lexer_t *mp_lexer_new_from_file(const char *filename) {
     mp_raise_OSError(MP_ENOENT);

ports/minimal/mpconfigport.h

@@ -11,31 +11,18 @@
 #define MICROPY_QSTR_EXTRA_POOL     mp_qstr_frozen_const_pool
 #define MICROPY_ALLOC_PATH_MAX      (256)
 #define MICROPY_ALLOC_PARSE_CHUNK_INIT (16)
-#define MICROPY_EMIT_X64            (0)
-#define MICROPY_EMIT_THUMB          (0)
-#define MICROPY_EMIT_INLINE_THUMB   (0)
-#define MICROPY_COMP_MODULE_CONST   (0)
 #define MICROPY_COMP_CONST          (0)
 #define MICROPY_COMP_DOUBLE_TUPLE_ASSIGN (0)
-#define MICROPY_COMP_TRIPLE_TUPLE_ASSIGN (0)
-#define MICROPY_MEM_STATS           (0)
-#define MICROPY_DEBUG_PRINTERS      (0)
 #define MICROPY_ENABLE_GC           (1)
 #define MICROPY_GC_ALLOC_THRESHOLD  (0)
-#define MICROPY_REPL_EVENT_DRIVEN   (0)
 #define MICROPY_HELPER_REPL         (1)
-#define MICROPY_HELPER_LEXER_UNIX   (0)
-#define MICROPY_ENABLE_SOURCE_LINE  (0)
-#define MICROPY_ENABLE_DOC_STRING   (0)
 #define MICROPY_ERROR_REPORTING     (MICROPY_ERROR_REPORTING_TERSE)
 #define MICROPY_BUILTIN_METHOD_CHECK_SELF_ARG (0)
 #define MICROPY_PY_ASYNC_AWAIT      (0)
 #define MICROPY_PY_BUILTINS_BYTEARRAY (0)
 #define MICROPY_PY_BUILTINS_DICT_FROMKEYS (0)
-#define MICROPY_PY_BUILTINS_MEMORYVIEW (0)
 #define MICROPY_PY_BUILTINS_ENUMERATE (0)
 #define MICROPY_PY_BUILTINS_FILTER  (0)
-#define MICROPY_PY_BUILTINS_FROZENSET (0)
 #define MICROPY_PY_BUILTINS_REVERSED (0)
 #define MICROPY_PY_BUILTINS_SET     (0)
 #define MICROPY_PY_BUILTINS_SLICE   (0)
@@ -48,34 +35,19 @@
 #define MICROPY_PY_ARRAY            (0)
 #define MICROPY_PY_ATTRTUPLE        (0)
 #define MICROPY_PY_COLLECTIONS      (0)
-#define MICROPY_PY_MATH             (0)
-#define MICROPY_PY_CMATH            (0)
 #define MICROPY_PY_IO               (0)
 #define MICROPY_PY_STRUCT           (0)
 #define MICROPY_PY_SYS              (0)
 #define MICROPY_MODULE_FROZEN_MPY   (1)
 #define MICROPY_CPYTHON_COMPAT      (0)
 #define MICROPY_MODULE_GETATTR      (0)
-#define MICROPY_LONGINT_IMPL        (MICROPY_LONGINT_IMPL_NONE)
-#define MICROPY_FLOAT_IMPL          (MICROPY_FLOAT_IMPL_NONE)
 
 // type definitions for the specific machine
 
-#define MICROPY_MAKE_POINTER_CALLABLE(p) ((void *)((mp_uint_t)(p) | 1))
-
-// This port is intended to be 32-bit, but unfortunately, int32_t for
-// different targets may be defined in different ways - either as int
-// or as long. This requires different printf formatting specifiers
-// to print such value. So, we avoid int32_t and use int directly.
-#define UINT_FMT "%u"
-#define INT_FMT "%d"
-typedef int mp_int_t; // must be pointer size
-typedef unsigned mp_uint_t; // must be pointer size
-
+typedef intptr_t mp_int_t; // must be pointer size
+typedef uintptr_t mp_uint_t; // must be pointer size
 typedef long mp_off_t;
 
-#define MP_PLAT_PRINT_STRN(str, len) mp_hal_stdout_tx_strn_cooked(str, len)
-
 // extra built in names to add to the global namespace
 #define MICROPY_PORT_BUILTINS \
     { MP_ROM_QSTR(MP_QSTR_open), MP_ROM_PTR(&mp_builtin_open_obj) },