Update version of nsync used by TensorFlow.
Update version of nsync used by TensorFlow.

TensorFlow previously imported nsync 1.25.0.
The changes to nsync since then are:
- a fix for a bug that can affect systems with weak memory
  ordering, such as Arm (the bug does not impact x86);
- a fix to a build problem when using both cmake on
  Windows with a compiler other than MSVC
  (previously, CMakeLists.txt would erroneously pass MSVC-specific
  warning-suppression flags to a non-MSVC  compiler);
- changes to help nsync work with thread sanitizer; and
- native atomic operation support for loongarch.
