Imported Upstream version 1.4upstream/1.4

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diff --git a/src/go/build/doc.go b/src/go/build/doc.go
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+// Copyright 2011 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 build gathers information about Go packages.
+//
+// Go Path
+//
+// The Go path is a list of directory trees containing Go source code.
+// It is consulted to resolve imports that cannot be found in the standard
+// Go tree.  The default path is the value of the GOPATH environment
+// variable, interpreted as a path list appropriate to the operating system
+// (on Unix, the variable is a colon-separated string;
+// on Windows, a semicolon-separated string;
+// on Plan 9, a list).
+//
+// Each directory listed in the Go path must have a prescribed structure:
+//
+// The src/ directory holds source code.  The path below 'src' determines
+// the import path or executable name.
+//
+// The pkg/ directory holds installed package objects.
+// As in the Go tree, each target operating system and
+// architecture pair has its own subdirectory of pkg
+// (pkg/GOOS_GOARCH).
+//
+// If DIR is a directory listed in the Go path, a package with
+// source in DIR/src/foo/bar can be imported as "foo/bar" and
+// has its compiled form installed to "DIR/pkg/GOOS_GOARCH/foo/bar.a"
+// (or, for gccgo, "DIR/pkg/gccgo/foo/libbar.a").
+//
+// The bin/ directory holds compiled commands.
+// Each command is named for its source directory, but only
+// using the final element, not the entire path.  That is, the
+// command with source in DIR/src/foo/quux is installed into
+// DIR/bin/quux, not DIR/bin/foo/quux.  The foo/ is stripped
+// so that you can add DIR/bin to your PATH to get at the
+// installed commands.
+//
+// Here's an example directory layout:
+//
+//	GOPATH=/home/user/gocode
+//
+//	/home/user/gocode/
+//	    src/
+//	        foo/
+//	            bar/               (go code in package bar)
+//	                x.go
+//	            quux/              (go code in package main)
+//	                y.go
+//	    bin/
+//	        quux                   (installed command)
+//	    pkg/
+//	        linux_amd64/
+//	            foo/
+//	                bar.a          (installed package object)
+//
+// Build Constraints
+//
+// A build constraint, also known as a build tag, is a line comment that begins
+//
+//	// +build
+//
+// that lists the conditions under which a file should be included in the package.
+// Constraints may appear in any kind of source file (not just Go), but
+// they must appear near the top of the file, preceded
+// only by blank lines and other line comments. These rules mean that in Go
+// files a build constraint must appear before the package clause.
+//
+// To distinguish build constraints from package documentation, a series of
+// build constraints must be followed by a blank line.
+//
+// A build constraint is evaluated as the OR of space-separated options;
+// each option evaluates as the AND of its comma-separated terms;
+// and each term is an alphanumeric word or, preceded by !, its negation.
+// That is, the build constraint:
+//
+//	// +build linux,386 darwin,!cgo
+//
+// corresponds to the boolean formula:
+//
+//	(linux AND 386) OR (darwin AND (NOT cgo))
+//
+// A file may have multiple build constraints. The overall constraint is the AND
+// of the individual constraints. That is, the build constraints:
+//
+//	// +build linux darwin
+//	// +build 386
+//
+// corresponds to the boolean formula:
+//
+//	(linux OR darwin) AND 386
+//
+// During a particular build, the following words are satisfied:
+//
+//	- the target operating system, as spelled by runtime.GOOS
+//	- the target architecture, as spelled by runtime.GOARCH
+//	- the compiler being used, either "gc" or "gccgo"
+//	- "cgo", if ctxt.CgoEnabled is true
+//	- "go1.1", from Go version 1.1 onward
+//	- "go1.2", from Go version 1.2 onward
+//	- "go1.3", from Go version 1.3 onward
+//	- "go1.4", from Go version 1.4 onward
+//	- any additional words listed in ctxt.BuildTags
+//
+// If a file's name, after stripping the extension and a possible _test suffix,
+// matches any of the following patterns:
+//	*_GOOS
+// 	*_GOARCH
+// 	*_GOOS_GOARCH
+// (example: source_windows_amd64.go) where GOOS and GOARCH represent
+// any known operating system and architecture values respectively, then
+// the file is considered to have an implicit build constraint requiring
+// those terms.
+//
+// To keep a file from being considered for the build:
+//
+//	// +build ignore
+//
+// (any other unsatisfied word will work as well, but ``ignore'' is conventional.)
+//
+// To build a file only when using cgo, and only on Linux and OS X:
+//
+//	// +build linux,cgo darwin,cgo
+//
+// Such a file is usually paired with another file implementing the
+// default functionality for other systems, which in this case would
+// carry the constraint:
+//
+//	// +build !linux,!darwin !cgo
+//
+// Naming a file dns_windows.go will cause it to be included only when
+// building the package for Windows; similarly, math_386.s will be included
+// only when building the package for 32-bit x86.
+//
+// Using GOOS=android matches build tags and files as for GOOS=linux
+// in addition to android tags and files.
+//
+package build