README.rst

Fix GCC 9.3 (using -O3) warnings on x86:

initconfig.c: In function ‘init_dump_ascii_wstr’:
initconfig.c:2679:34: warning: format ‘%lc’ expects argument of type
‘wint_t’, but argument 2 has type ‘wchar_t’ {aka ‘long int’}
 2679 |             PySys_WriteStderr("%lc", ch);
initconfig.c:2682:38: warning: format ‘%x’ expects argument of type
‘unsigned int’, but argument 2 has type ‘wchar_t’ {aka ‘long int’}
 2682 |             PySys_WriteStderr("\\x%02x", ch);
initconfig.c:2686:38: warning: format ‘%x’ expects argument of type
‘unsigned int’, but argument 2 has type ‘wchar_t’ {aka ‘long int’}
 2686 |             PySys_WriteStderr("\\U%08x", ch);
initconfig.c:2690:38: warning: format ‘%x’ expects argument of type
‘unsigned int’, but argument 2 has type ‘wchar_t’ {aka ‘long int’}
 2690 |             PySys_WriteStderr("\\u%04x", ch);
(cherry picked from commit 640e8e1d)

Co-authored-by: Victor Stinner <vstinner@python.org>