cmd/compile/internal/ssa: hide gen packge from ./make.bash

Fixes #15122

Change-Id: Ie2c802d78aea731e25bf4b193b3c2e4c884e0573
Reviewed-on: https://go-review.googlesource.com/21524
Run-TryBot: Dave Cheney <dave@cheney.net>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
diff --git a/src/cmd/compile/internal/ssa/gen/genericOps.go b/src/cmd/compile/internal/ssa/gen/genericOps.go
index d8632a9..e6a0e83 100644
--- a/src/cmd/compile/internal/ssa/gen/genericOps.go
+++ b/src/cmd/compile/internal/ssa/gen/genericOps.go
@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
+// +build ignore
+
 package main
 
 // Generic opcodes typically specify a width. The inputs and outputs