doc/go1.16: document GO386=387 and GO386=softfloat

Also add a few more TODOs as found by the relnote command.
It's an incomplete list due to #41849.

For #40700.

Change-Id: Id17a9be86d3338e1fcb281d26e7298ff26e92864
Reviewed-on: https://go-review.googlesource.com/c/go/+/260337
Reviewed-by: Ian Lance Taylor <[email protected]>
Trust: Dmitri Shuralyov <[email protected]>

Author: dmitshur

doc/go1.16.html

@@ -38,6 +38,17 @@ <h3 id="netbsd">NetBSD</h3>
   <code>netbsd/arm64</code> port).
 </p>
 
+<h3 id="386">386</h3>
+
+<p><!-- golang.org/issue/40255, golang.org/issue/41848, CL 258957, and CL 260017 -->
+  As <a href="go1.15#386">announced</a> in the Go 1.15 release notes,
+  Go 1.16 drops support for x87 mode compilation (<code>GO386=387</code>).
+  Support for non-SSE2 processors is now available using soft float
+  mode (<code>GO386=softfloat</code>).
+  Users running on non-SSE2 processors should replace <code>GO386=387</code>
+  with <code>GO386=softfloat</code>.
+</p>
+
 <h2 id="tools">Tools</h2>
 
 <p>
@@ -162,6 +173,8 @@ <h2 id="linker">Linker</h2>
   TODO: update with final numbers later in the release.
 </p>
 
+<!-- CL 255259: https://golang.org/cl/255259: cmd/link: enable ASLR on windows binaries built with -buildmode=c-shared -->
+
 <h2 id="library">Core library</h2>
 
 <p>
@@ -275,3 +288,11 @@ <h3 id="minor_library_changes">Minor changes to the library</h3>
     </p>
   </dd>
 </dl><!-- net/http -->
+
+<dl id="runtime/debug"><dt><a href="/pkg/runtime/debug/">runtime/debug</a></dt>
+  <dd>
+    <p><!-- CL 249677 -->
+      TODO: <a href="https://golang.org/cl/249677">https://golang.org/cl/249677</a>: provide Addr method for errors from SetPanicOnFault
+    </p>
+  </dd>
+</dl><!-- runtime/debug -->