runtime: renamed os2_linux.go to os2_linux_generic.go, added mips64 support

Linux/mips64 has a different sigset type and some different constants.
os2_linux.go is renamed to os2_linux_generic.go, and not used in mips64.
The corresponding file os2_linux_mips64x.go is added.

Change-Id: Ief83845a2779f7fe048d236d3c7da52b627ab533
Reviewed-on: https://go-review.googlesource.com/14992
Reviewed-by: Minux Ma <minux@golang.org>

src/runtime/os2_linux_generic.go

@@ -2,6 +2,10 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
+// +build !mips64
+// +build !mips64le
+// +build linux
+
 package runtime
 
 const (

src/runtime/os2_linux_mips64x.go

@@ -0,0 +1,25 @@
+// Copyright 2015 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 linux
+// +build mips64 mips64le
+
+package runtime
+
+const (
+	_SS_DISABLE  = 2
+	_NSIG        = 65
+	_SI_USER     = 0
+	_SIG_BLOCK   = 1
+	_SIG_UNBLOCK = 2
+	_SIG_SETMASK = 3
+	_RLIMIT_AS   = 6
+)
+
+type sigset [2]uint64
+
+type rlimit struct {
+	rlim_cur uintptr
+	rlim_max uintptr
+}