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/binascii.c b/Modules/binascii.c
index 19681b4..74db739 100644
--- a/Modules/binascii.c
+++ b/Modules/binascii.c
@@ -1099,7 +1099,7 @@
 static int
 to_int(int c)
 {
-    if (isdigit(c))
+    if (Py_ISDIGIT(c))
         return c - '0';
     else {
         if (Py_ISUPPER(c))