[runtime] Fix runtime tracing compile failure on gcc (#19642)

When compiling with gcc I'm getting an error due to the definition of
`std::atomic<uint32_t> next_tracing_thread_i` having a different
language linkage than the declaration:

```
iree/runtime/src/iree/base/tracing/tracy.cc:468:23: error: conflicting declaration of ‘std::atomic<unsigned int> iree_tracing_context_t::next_tracing_thread_id’ with ‘C’ linkage
```

Strangely, clang seems to be fine with this [godbolt gcc vs
clang](https://godbolt.org/z/Yhfcjhchd).

Signed-off-by: Ian Wood <ianwood2024@u.northwestern.edu>

runtime/src/iree/base/tracing/tracy.cc

diff --git a/runtime/src/iree/base/tracing/tracy.cc b/runtime/src/iree/base/tracing/tracy.cc
index 129fb75..a38f8c4 100644
--- a/runtime/src/iree/base/tracing/tracy.cc
+++ b/runtime/src/iree/base/tracing/tracy.cc
@@ -452,7 +452,7 @@
 #if IREE_TRACING_EXPERIMENTAL_CONTEXT_API
 
 struct iree_tracing_context_t {
-  static std::atomic<uint32_t> next_tracing_thread_id;
+  inline static std::atomic<uint32_t> next_tracing_thread_id{0x80000000u};
   tracy::moodycamel::ProducerToken token_detail;
   tracy::ProducerWrapper token;
   uint32_t thread_id = 0;
@@ -464,10 +464,6 @@
   }
 };
 
-// static
-std::atomic<uint32_t> iree_tracing_context_t::next_tracing_thread_id{
-    0x80000000u};
-
 #define IREE_TRACING_CONTEXT_BEGIN_WRITE(context, queue_type)             \
   tracy::moodycamel::ConcurrentQueueDefaultTraits::index_t __magic;       \
   tracy::moodycamel::ConcurrentQueue<tracy::QueueItem>::ExplicitProducer* \