cpu: add linux/ppc64x

Port from Go internal/cpu.

Fixes golang/go#25185

Change-Id: Id3cac18da6ffec9d10df755c4032ce3068ab634d
Reviewed-on: https://go-review.googlesource.com/c/152938
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

cpu/cpu_test.go

@@ -38,3 +38,17 @@ func TestARM64minimalFeatures(t *testing.T) {
 		t.Fatal("HasFP expected true, got false")
 	}
 }
+
+// On ppc64x, the ISA bit for POWER8 should always be set on POWER8 and beyond.
+func TestPPC64minimalFeatures(t *testing.T) {
+	// Do not run this with gccgo on ppc64, as it doesn't have POWER8 as a minimum
+	// requirement.
+	if runtime.Compiler == "gccgo" && runtime.GOARCH == "ppc64" {
+		t.Skip("gccgo does not require POWER8 on ppc64; skipping")
+	}
+	if runtime.GOARCH == "ppc64" || runtime.GOARCH == "ppc64le" {
+		if !cpu.PPC64.IsPOWER8 {
+			t.Fatal("IsPOWER8 expected true, got false")
+		}
+	}
+}