libgo: fix getrandom build for 32-bit ppc

    
    Add a ppc build constraint for internal/syscall/unix.
    
    Reviewed-on: https://go-review.googlesource.com/25547

From-SVN: r239210

gcc/go/gofrontend/MERGE

-8473b709ebd46c03c0e36e140656bd8c5d32d883
+b50a0c3fa975186f934b76e25dae42eb65148d67
 
 The first line of this file holds the git revision number of the last
 merge done from the gofrontend repository.

libgo/go/internal/syscall/unix/getrandom_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