[HWASan] add comment to explain why we can use __has_feature

Bug: 276930343
Change-Id: I0b3e152269a147f67cae3c534be92ee169fe393b
diff --git a/libc/bionic/heap_tagging.cpp b/libc/bionic/heap_tagging.cpp
index be21e0c..230899a 100644
--- a/libc/bionic/heap_tagging.cpp
+++ b/libc/bionic/heap_tagging.cpp
@@ -208,6 +208,9 @@
   }
 #endif  // __aarch64__
 
+  // We can use __has_feature here rather than __hwasan_handle_longjmp as a
+  // weak symbol because this is part of libc which is always sanitized for a
+  // hwasan enabled process.
 #if __has_feature(hwaddress_sanitizer)
   __hwasan_handle_longjmp(sp_dst);
 #endif  // __has_feature(hwaddress_sanitizer)