internal/syscall/unix: restore ppc build tag

It was accidentally lost in the 1.15rc1 merge.

Fixes GCC PR 96567

Change-Id: I99a0befa993c0b690c32bf787ff6888c3dd591af
Reviewed-on: https://go-review.googlesource.com/c/gofrontend/+/247843
Reviewed-by: Than McIntosh <thanm@google.com>
diff --git a/libgo/go/internal/syscall/unix/sysnum_linux_ppc64x.go b/libgo/go/internal/syscall/unix/sysnum_linux_ppc64x.go
index 576937e..aa2e81a 100644
--- a/libgo/go/internal/syscall/unix/sysnum_linux_ppc64x.go
+++ b/libgo/go/internal/syscall/unix/sysnum_linux_ppc64x.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 ppc64 ppc64le
+// +build ppc ppc64 ppc64le
 
 package unix