syscall: freeze the package
Add a clause to the doc comment for the package and a
paragraph in the compatibility document explaining the
situation.
LGTM=bradfitz, adg, rsc
R=golang-codereviews, adg, bradfitz, minux, rsc
CC=golang-codereviews
https://golang.org/cl/129820043
diff --git a/doc/go1compat.html b/doc/go1compat.html
index d10b9af..2c8d214 100644
--- a/doc/go1compat.html
+++ b/doc/go1compat.html
@@ -152,6 +152,20 @@
with the Go 1 point releases.
</p>
+<h2 id="operating_systems">Operating systems</h2>
+
+<p>
+It is impossible to guarantee long-term compatibility with operating
+system interfaces, which are changed by outside parties.
+The <a href="/pkg/syscall/"><code>syscall</code></a> package
+is therefore outside the purview of the guarantees made here.
+As of Go version 1.4, the <code>syscall</code> package is frozen.
+Any evolution of the system call interface must be supported elsewhere,
+such as in the <code>go.sys</code> subrepository.
+For details and background, see
+<a href="https://golang.org/s/go1.4-syscall">this document</a>.
+</p>
+
<h2 id="tools">Tools</h2>
<p>
