Issue #16330: Use surrogate-related macros

Patch written by Serhiy Storchaka.
diff --git a/Python/fileutils.c b/Python/fileutils.c
index 501cb8c..526751d 100644
--- a/Python/fileutils.c
+++ b/Python/fileutils.c
@@ -85,7 +85,7 @@
             /* Only use the result if it contains no
                surrogate characters. */
             for (tmp = res; *tmp != 0 &&
-                         (*tmp < 0xd800 || *tmp > 0xdfff); tmp++)
+                         !Py_UNICODE_IS_SURROGATE(*tmp); tmp++)
                 ;
             if (*tmp == 0) {
                 if (size != NULL)
@@ -131,7 +131,7 @@
             memset(&mbs, 0, sizeof mbs);
             continue;
         }
-        if (*out >= 0xd800 && *out <= 0xdfff) {
+        if (Py_UNICODE_IS_SURROGATE(*out)) {
             /* Surrogate character.  Escape the original
                byte sequence with surrogateescape. */
             argsize -= converted;