Update version of nsync used by TensorFlow to version 1.29.2

TensorFlow previously imported nsync 1.27.0.

The changes to nsync since then are:

- An update the the bazel BUILD file to use the "@platforms" mechanism to
  select source code depending on architecture and operating system.
  (Strangely, the "@platforms" mechanism still doesn't accommodate
  compiler-specific parameterization.  It is accommodated using the
  "@bazel_tools//tools/cpp:compiler" setting.)

- A change to CMakeLists.txt to add export targets for the C and C++ libraries.

- A fix in nsync_semaphore_futex.c to allow the use of 64-bit time_t on 32-bit
  Linux systems, and to allow compilation to succeed for 32-bit RISC-V,
  which supports only 64-bit time_t (unlike most 32-bit Linux systems).

- A fix to include stdlib.h in the Windows-specific file
  nsync_semaphore_win32.c, to avoid a compiler warning.

PiperOrigin-RevId: 646202486

third_party/nsync.patch

@@ -6,4 +6,4 @@ index 53cc1a6..0000000
 --- a/VERSION
 +++ /dev/null
 @@ -1 +0,0 @@
--1.27.0
+-1.29.2

workspace2.bzl

@@ -297,10 +297,10 @@ def _tf_repositories():
     tf_http_archive(
         name = "nsync",
         patch_file = ["//third_party:nsync.patch"],
-        sha256 = "e8e552a358f4a28e844207a7c5cb51767e4aeb0b29e22d23ac2a09924130f761",
-        strip_prefix = "nsync-1.27.0",
+        sha256 = "1d63e967973733d2c97e841e3c05fac4d3fa299f01d14c86f2695594c7a4a2ec",
+        strip_prefix = "nsync-1.29.2",
         system_build_file = "//third_party/systemlibs:nsync.BUILD",
-        urls = tf_mirror_urls("https://github.com/google/nsync/archive/1.27.0.tar.gz"),
+        urls = tf_mirror_urls("https://github.com/google/nsync/archive/1.29.2.tar.gz"),
     )
 
     tf_http_archive(