patch 8.0.1635: undefining _POSIX_THREADS causes problems with Python 3

Problem:    Undefining _POSIX_THREADS causes problems with Python 3. (Micah
            Bucy, closes #2748)
Solution:   Remove the lines.
diff --git a/src/if_python3.c b/src/if_python3.c
index 02d9134..59c115d 100644
--- a/src/if_python3.c
+++ b/src/if_python3.c
@@ -34,11 +34,6 @@
 
 #include <limits.h>
 
-/* Python.h defines _POSIX_THREADS itself (if needed) */
-#ifdef _POSIX_THREADS
-# undef _POSIX_THREADS
-#endif
-
 #if defined(_WIN32) && defined(HAVE_FCNTL_H)
 # undef HAVE_FCNTL_H
 #endif
diff --git a/src/version.c b/src/version.c
index ca668c1..b2959e3 100644
--- a/src/version.c
+++ b/src/version.c
@@ -767,6 +767,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    1635,
+/**/
     1634,
 /**/
     1633,