Issue #17173: Remove uses of locale-dependent C functions (isalpha() etc.) in the interpreter.

I've left a couple of them in: zlib (third-party lib), getaddrinfo.c
(doesn't include Python.h, and probably obsolete), _sre.c (legitimate
use for the re.LOCALE flag).

Modules/socketmodule.c

@@ -519,7 +519,7 @@ set_error(void)
                 /* If non-empty msg, trim CRLF */
                 char *lastc = &outbuf[ strlen(outbuf)-1 ];
                 while (lastc > outbuf &&
-                       isspace(Py_CHARMASK(*lastc))) {
+                       Py_ISSPACE(Py_CHARMASK(*lastc))) {
                     /* Trim trailing whitespace (CRLF) */
                     *lastc-- = '\0';
                 }