Merge #12973 itertools fix.

diff --cc Misc/NEWS
index 0e18621d2399fe5385c97f85ff8049461889b351,1b0373663ea861ae7b41d354a5cf5d407028f079..4f550340e7fabfe94c4f59ad67c7b69be84cd9fb
--- 1/Misc/NEWS
--- 2/Misc/NEWS
+++ b/Misc/NEWS
@@@ -17,13 -17,10 +17,13 @@@ Core and Builtin
  - Issue #13021: Missing decref on an error path.  Thanks to Suman Saha for
    finding the bug and providing a patch.
  
- - Issue #12973: Fix overflow check that relied on undefined behaviour in
-   list_repeat.  This bug caused test_list to fail with recent versions
-   of Clang.
+ - Issue #12973: Fix overflow checks that relied on undefined behaviour in
+   list_repeat (listobject.c) and islice_next (itertoolsmodule.c).  These bugs
+   caused test failures with recent versions of Clang.
  
 +- Issue #12904: os.utime, os.futimes, os.lutimes, and os.futimesat now write
 +  atime and mtime with nanosecond precision on modern POSIX platforms.
 +
  - Issue #12802: the Windows error ERROR_DIRECTORY (numbered 267) is now
    mapped to POSIX errno ENOTDIR (previously EINVAL).
  

diff --cc Modules/itertoolsmodule.c
Simple merge