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).
diff --git a/Modules/_struct.c b/Modules/_struct.c
index edbe9b9..3f20518 100644
--- a/Modules/_struct.c
+++ b/Modules/_struct.c
@@ -1184,7 +1184,7 @@
     size = 0;
     len = 0;
     while ((c = *s++) != '\0') {
-        if (isspace(Py_CHARMASK(c)))
+        if (Py_ISSPACE(Py_CHARMASK(c)))
             continue;
         if ('0' <= c && c <= '9') {
             num = c - '0';
@@ -1249,7 +1249,7 @@
     s = fmt;
     size = 0;
     while ((c = *s++) != '\0') {
-        if (isspace(Py_CHARMASK(c)))
+        if (Py_ISSPACE(Py_CHARMASK(c)))
             continue;
         if ('0' <= c && c <= '9') {
             num = c - '0';