cmd/viewcore: skip build on aix

./cmd/viewcore depends on github.com/chzyer/readline,
which doesn't build on aix yet.

Updates golang/go#32839

Change-Id: I918667fcbc48a2ed5e8bb550be962932ccc8131d
Reviewed-on: https://go-review.googlesource.com/c/debug/+/192322
Run-TryBot: Bryan C. Mills <bcmills@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Hyang-Ah Hana Kim <hyangah@gmail.com>

cmd/viewcore/html.go

@@ -2,6 +2,9 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
+// +build !aix
+// (https://golang.org/issue/32839)
+
 package main
 
 import (

cmd/viewcore/main.go

@@ -2,6 +2,11 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
+// Skip aix for now: github.com/chzyer/readline doesn't support it.
+// (https://golang.org/issue/32839)
+//
+// +build !aix
+
 // The viewcore tool is a command-line tool for exploring the state of a Go process
 // that has dumped core.
 // Run "viewcore help" for a list of commands.