libgo: update to Go 1.8 release candidate 1

Compiler changes:
      * Change map assignment to use mapassign and assign value directly.
      * Change string iteration to use decoderune, faster for ASCII strings.
      * Change makeslice to take int, and use makeslice64 for larger values.
      * Add new noverflow field to hmap struct used for maps.
    
    Unresolved problems, to be fixed later:
      * Commented out test in go/types/sizes_test.go that doesn't compile.
      * Commented out reflect.TestStructOf test for padding after zero-sized field.
    
    Reviewed-on: https://go-review.googlesource.com/35231

gotools/:
	Updates for Go 1.8rc1.
	* Makefile.am (go_cmd_go_files): Add bug.go.
	(s-zdefaultcc): Write defaultPkgConfig.
	* Makefile.in: Rebuild.

From-SVN: r244456

libgo/go/net/fd_io_plan9.go

@@ -0,0 +1,93 @@
+// Copyright 2016 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.
+
+package net
+
+import (
+	"os"
+	"runtime"
+	"sync"
+	"syscall"
+)
+
+// asyncIO implements asynchronous cancelable I/O.
+// An asyncIO represents a single asynchronous Read or Write
+// operation. The result is returned on the result channel.
+// The undergoing I/O system call can either complete or be
+// interrupted by a note.
+type asyncIO struct {
+	res chan result
+
+	// mu guards the pid field.
+	mu sync.Mutex
+
+	// pid holds the process id of
+	// the process running the IO operation.
+	pid int
+}
+
+// result is the return value of a Read or Write operation.
+type result struct {
+	n   int
+	err error
+}
+
+// newAsyncIO returns a new asyncIO that performs an I/O
+// operation by calling fn, which must do one and only one
+// interruptible system call.
+func newAsyncIO(fn func([]byte) (int, error), b []byte) *asyncIO {
+	aio := &asyncIO{
+		res: make(chan result, 0),
+	}
+	aio.mu.Lock()
+	go func() {
+		// Lock the current goroutine to its process
+		// and store the pid in io so that Cancel can
+		// interrupt it. We ignore the "hangup" signal,
+		// so the signal does not take down the entire
+		// Go runtime.
+		runtime.LockOSThread()
+		runtime_ignoreHangup()
+		aio.pid = os.Getpid()
+		aio.mu.Unlock()
+
+		n, err := fn(b)
+
+		aio.mu.Lock()
+		aio.pid = -1
+		runtime_unignoreHangup()
+		aio.mu.Unlock()
+
+		aio.res <- result{n, err}
+	}()
+	return aio
+}
+
+var hangupNote os.Signal = syscall.Note("hangup")
+
+// Cancel interrupts the I/O operation, causing
+// the Wait function to return.
+func (aio *asyncIO) Cancel() {
+	aio.mu.Lock()
+	defer aio.mu.Unlock()
+	if aio.pid == -1 {
+		return
+	}
+	proc, err := os.FindProcess(aio.pid)
+	if err != nil {
+		return
+	}
+	proc.Signal(hangupNote)
+}
+
+// Wait for the I/O operation to complete.
+func (aio *asyncIO) Wait() (int, error) {
+	res := <-aio.res
+	return res.n, res.err
+}
+
+// The following functions, provided by the runtime, are used to
+// ignore and unignore the "hangup" signal received by the process.
+func runtime_ignoreHangup()
+func runtime_unignoreHangup()