crypto/bn256: fix issues caused by Go 1.11

vendor/golang.org/x/sys/cpu/cpu_gccgo.go

@@ -0,0 +1,26 @@
+// Copyright 2018 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// +build 386 amd64 amd64p32
+// +build gccgo
+
+package cpu
+
+//extern gccgoGetCpuidCount
+func gccgoGetCpuidCount(eaxArg, ecxArg uint32, eax, ebx, ecx, edx *uint32)
+
+func cpuid(eaxArg, ecxArg uint32) (eax, ebx, ecx, edx uint32) {
+	var a, b, c, d uint32
+	gccgoGetCpuidCount(eaxArg, ecxArg, &a, &b, &c, &d)
+	return a, b, c, d
+}
+
+//extern gccgoXgetbv
+func gccgoXgetbv(eax, edx *uint32)
+
+func xgetbv() (eax, edx uint32) {
+	var a, d uint32
+	gccgoXgetbv(&a, &d)
+	return a, d
+}