doc/go1.19: some platforms are still on TSAN v2

For #51400

Change-Id: Ie6d6ac773aa81b105e15ef7399374f574197d775
Reviewed-on: https://go-review.googlesource.com/c/go/+/410817
Reviewed-by: Cherry Mui <[email protected]>

Author: aclements

doc/go1.19.html

@@ -703,14 +703,23 @@ <h3 id="minor_library_changes">Minor changes to the library</h3>
   <dd>
     <p><!-- https://go.dev/issue/49761 --><!-- CL 333529 -->
       The race detector has been upgraded to use thread sanitizer
-      version v3. Compared to v2, it is now typically 1.5x to 2x
-      faster, uses half as much memory, and it supports an unlimited
-      number of goroutines.
+      version v3 on all supported platforms
+      except <code>windows/amd64</code>
+      and <code>openbsd/amd64</code>, which remain on v2.
+      Compared to v2, it is now typically 1.5x to 2x faster, uses half
+      as much memory, and it supports an unlimited number of
+      goroutines.
     </p>
 
     <p><!-- CL 336549 -->
       The race detector is now supported on <code>GOARCH=s390x</code>.
     </p>
+
+    <p><!-- https://go.dev/issue/52090 -->
+      Race detector support for <code>openbsd/amd64</code> has been
+      removed from thread sanitizer upstream, so it is unlikely to
+      ever be updated from v2.
+    </p>
   </dd>
 </dl><!-- runtime/race -->