[libc++abi] Use __has_feature check to enable usage of thread_local for exception storage (#97591)

Previously, we'd use HAS_THREAD_LOCAL which was never defined. Hence,
we'd basically never use the code path where we use thread_local.

Fixes #78207

Author: ldionne

libcxxabi/src/cxa_exception_storage.cpp

@@ -24,7 +24,7 @@ extern "C" {
 } // extern "C"
 } // namespace __cxxabiv1
 
-#elif defined(HAS_THREAD_LOCAL)
+#elif __has_feature(cxx_thread_local)
 
 namespace __cxxabiv1 {
 namespace {