[release-branch.go1.12] doc: document Go 1.12.3

Change-Id: I84c9a8ddbd3101dd478e4a8a4e191863e68c6af6
Reviewed-on: https://go-review.googlesource.com/c/go/+/171140Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
(cherry picked from commit 8759b4d3)
Reviewed-on: https://go-review.googlesource.com/c/go/+/171141

doc/devel/release.html

@@ -48,6 +48,14 @@ command, the runtime, and the <code>doc</code>, <code>net</code>,
 1.12.2 milestone</a> on our issue tracker for details.
 </p>
 
+<p>
+go1.12.3 (released 2019/04/08) fixes an issue where using the prebuilt binary
+releases on older versions of GNU/Linux
+<a href="https://golang/go/issues/31293">led to failures</a>
+when linking programs that used cgo.
+Only Linux users who hit this issue need to update.
+</p>
+
 <h2 id="go1.11">go1.11 (released 2018/08/24)</h2>
 
 <p>