cmd/go: add AIX operating system

This commit adds AIX operating system to cmd/go package for ppc64
architecture.

Updates: #25893

Change-Id: I2605d10a7833fa2eb197f6db4a52d5919cf93614
Reviewed-on: https://go-review.googlesource.com/c/138732
Run-TryBot: Tobias Klauser <tobias.klauser@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

src/cmd/go/internal/base/signal_unix.go

@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// +build darwin dragonfly freebsd js linux nacl netbsd openbsd solaris
+// +build aix darwin dragonfly freebsd js linux nacl netbsd openbsd solaris
 
 package base
 

src/cmd/go/internal/work/exec.go

@@ -1648,6 +1648,7 @@ func (b *Builder) cover(a *Action, dst, src string, varName string) error {
 
 var objectMagic = [][]byte{
 	{'!', '<', 'a', 'r', 'c', 'h', '>', '\n'}, // Package archive
+	{'<', 'b', 'i', 'g', 'a', 'f', '>', '\n'}, // Package AIX big archive
 	{'\x7F', 'E', 'L', 'F'},                   // ELF
 	{0xFE, 0xED, 0xFA, 0xCE},                  // Mach-O big-endian 32-bit
 	{0xFE, 0xED, 0xFA, 0xCF},                  // Mach-O big-endian 64-bit
@@ -1658,6 +1659,8 @@ var objectMagic = [][]byte{
 	{0x00, 0x00, 0x8a, 0x97},                  // Plan 9 amd64
 	{0x00, 0x00, 0x06, 0x47},                  // Plan 9 arm
 	{0x00, 0x61, 0x73, 0x6D},                  // WASM
+	{0x01, 0xDF},                              // XCOFF 32bit
+	{0x01, 0xF7},                              // XCOFF 64bit
 }
 
 func isObject(s string) bool {