bpo-29240, bpo-32030: Py_Main() re-reads config if encoding changes (#4899)

bpo-29240, bpo-32030: If the encoding change (C locale coerced or
UTF-8 Mode changed), Py_Main() now reads again the configuration with
the new encoding.

Changes:

* Add _Py_UnixMain() called by main().
* Rename pymain_free_pymain() to pymain_clear_pymain(), it can now be
  called multipled times.
* Rename pymain_parse_cmdline_envvars() to pymain_read_conf().
* Py_Main() now clears orig_argc and orig_argv at exit.
* Remove argv_copy2, Py_Main() doesn't modify argv anymore. There is
  no need anymore to get two copies of the wchar_t** argv.
* _PyCoreConfig: add coerce_c_locale and coerce_c_locale_warn.
* Py_UTF8Mode is now initialized to -1.
* Locale coercion (PEP 538) now respects -I and -E options.

Modules/getpath.c

@@ -112,7 +112,7 @@ extern "C" {
 
 #define DECODE_LOCALE_ERR(NAME, LEN) \
     ((LEN) == (size_t)-2) \
-     ? _Py_INIT_USER_ERR("cannot decode " #NAME) \
+     ? _Py_INIT_USER_ERR("cannot decode " NAME) \
      : _Py_INIT_NO_MEMORY()
 
 typedef struct {