[compiler-rt][hwasan][fuchsia] Implement InitializeOsSupport

[leonardchan]

Summary

This is empty for now, but we will add a check that TBI is enabled once the tagged pointer ABI for zircon is finalized. This depends on D105667.

[mcgrathr]

lgtm with fxbug.dev/NNN url ref added.

compiler-rt/lib/hwasan/hwasan_fuchsia.cpp

175

Please make a public bug on fxbug.dev about the Zircon TBI ABI and then point to it in the comment here.

compiler-rt/lib/hwasan/hwasan_fuchsia.cpp

 void HwasanTSDInit() {}
 void HwasanTSDThreadInit() {}
 
 // On linux, this just would call `atexit(HwasanAtExit)`. The functions in
 // HwasanAtExit are unimplemented for Fuchsia and effectively no-ops, so this
 // function is unneeded.
 void InstallAtExitHandler() {}
 
+// TODO(fxbug.dev/81499): Once we finalize the tagged pointer ABI in zircon, we should come back
+// here and implement the appropriate check that TBI is enabled.
+void InitializeOsSupport() {}
+
 }  // namespace __hwasan
 
 extern "C" {
 
 void *__sanitizer_before_thread_create_hook(thrd_t thread, bool detached,
                                             const char *name, void *stack_base,
                                             size_t stack_size) {
   return __hwasan::BeforeThreadCreateHook(