runtime: add getproccount for hurd

Patch by Svante Signell.
    
    Reviewed-on: https://go-review.googlesource.com/c/160825

From-SVN: r268463

gcc/go/gofrontend/MERGE

@@ -1,4 +1,4 @@
-51fb93fd71b8a0a690455dfdd3d12b2aa0171f5c
+582392b80c07bd7e830e177b775dc4ef802b5fd6
 
 The first line of this file holds the git revision number of the last
 merge done from the gofrontend repository.

libgo/runtime/getncpu-hurd.c

@@ -0,0 +1,16 @@
+// Copyright 2012 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.
+
+#include <unistd.h>
+
+#include "runtime.h"
+#include "defs.h"
+
+int32
+getproccount(void)
+{
+	int32 n;
+	n = (int32)sysconf(_SC_NPROCESSORS_ONLN);
+	return n > 1 ? n : 1;
+}