Revert "test: do not run external linking test on ppc64le"

Broke most builders.

This reverts commit a60c5366.

Change-Id: Iae952cfcc73ef5da621616a0b3d586b60d1ce9c9
Reviewed-on: https://go-review.googlesource.com/12684Reviewed-by: Russ Cox <rsc@golang.org>

test/fixedbugs/issue10607.go

 // +build linux
-// +build !ppc64,!ppc64le
 // run
 
 // Copyright 2015 The Go Authors. All rights reserved.