doc/go1.19: add release notes for syscall

For #51400

Change-Id: If5fc131df254d47a989ff61c8e584cb8149cbd09
Reviewed-on: https://go-review.googlesource.com/c/go/+/410116
Reviewed-by: Michael Knyszek <mknyszek@google.com>
Run-TryBot: Michael Pratt <mpratt@google.com>

Author: prattmic

doc/go1.19.html

@@ -412,6 +412,24 @@ <h3 id="minor_library_changes">Minor changes to the library</h3>
   </dd>
 </dl><!-- strconv -->
 
+<dl id="syscall"><dt><a href="/pkg/syscall/">syscall</a></dt>
+  <dd>
+    <p><!-- https://go.dev/issue/51192 --><!-- CL 385796 -->
+      On PowerPC (<code>GOARCH=ppc64</code>, <code>ppc64le</code>),
+      <a href="/pkg/syscall/#Syscall"><code>Syscall</code></a>,
+      <a href="/pkg/syscall/#Syscall6"><code>Syscall6</code></a>,
+      <a href="/pkg/syscall/#RawSyscall"><code>RawSyscall</code></a>, and
+      <a href="/pkg/syscall/#RawSyscall6"><code>RawSyscall6</code></a>
+      now always return 0 for return value <code>r2</code> instead of an
+      undefined value.
+    </p>
+
+    <p><!-- CL 391434 -->
+      On AIX and Solaris, <code>Getrusage</code> is now defined.
+    </p>
+  </dd>
+</dl><!-- syscall -->
+
 <dl id="time"><dt><a href="/pkg/time/">time</a></dt>
   <dd>
     <p><!-- CL 393515 -->