http2/h2i: disable building h2i on plan9 and solaris

They lack terminal.MakeRaw and terminal.Restore.

Updates golang/go#11811

Change-Id: I1e5d8ca90b2f9c13fe7a6396c2f86e0a5b392b84
Reviewed-on: https://go-review.googlesource.com/18577
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-by: Chris Broadfoot <cbro@golang.org>

http2/h2i/h2i.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 !plan9,!solaris
+
 /*
 The h2i command is an interactive HTTP/2 console.