[third-party] Silence warning on benchmark when building with Clang ToT

fixes:
```
[7409/7446] Building CXX object third-party\benchmark\src\CMakeFiles\benchmark.dir\benchmark.cc.obj
C:\git\llvm-project\third-party\benchmark\src\benchmark.cc(172,17): warning: offset of on non-standard-layout type 'State' [-Winvalid-offsetof]
  172 |   static_assert(offsetof(State, error_occurred_) <=
      |                 ^               ~~~~~~~~~~~~~~~
C:\git\llvm_package_18.0.0\build64_stage0\lib\clang\18\include\__stddef_offsetof.h(11,24): note: expanded from macro 'offsetof'
   11 | #define offsetof(t, d) __builtin_offsetof(t, d)
      |                        ^                     ~
1 warning generated.
```

third-party/benchmark/src/benchmark.cc

@@ -166,6 +166,9 @@ State::State(IterationCount max_iters, const std::vector<int64_t>& ranges,
 #elif defined(__GNUC__)
 #pragma GCC diagnostic push
 #pragma GCC diagnostic ignored "-Winvalid-offsetof"
+#elif defined(__clang__)
+#pragma clang diagnostic push
+#pragma clang diagnostic ignored "-Winvalid-offsetof"
 #endif
   // Offset tests to ensure commonly accessed data is on the first cache line.
   const int cache_line_size = 64;
@@ -176,6 +179,8 @@ State::State(IterationCount max_iters, const std::vector<int64_t>& ranges,
 #pragma warning pop
 #elif defined(__GNUC__)
 #pragma GCC diagnostic pop
+#elif defined(__clang__)
+#pragma clang diagnostic pop
 #endif
 }