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/posixmodule.c b/Modules/posixmodule.c
index 4179c0e..67bff25 100644
--- a/Modules/posixmodule.c
+++ b/Modules/posixmodule.c
@@ -695,7 +695,7 @@
     if (strlen(msgbuf) > 0) { /* If Non-Empty Msg, Trim CRLF */
         char *lastc = &msgbuf[ strlen(msgbuf)-1 ];
 
-        while (lastc > msgbuf && isspace(Py_CHARMASK(*lastc)))
+        while (lastc > msgbuf && Py_ISSPACE(Py_CHARMASK(*lastc)))
             *lastc-- = '\0'; /* Trim Trailing Whitespace (CRLF) */
     }