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Contains ad hoc patches for cross building.

From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: Boris Nagaev <bnagaev@gmail.com>
Date: Sat, 25 Jun 2016 13:51:06 +0200
Subject: [PATCH] cgo: add environmental variable override for pkg-config

Allow overriding default name of `pkg-config` utility via
environmental variable PKG_CONFIG (same as used by autoconf
pkg.m4 macros). This facilitates easy cross-compilation of cgo
code.

Original patch against Go <= 1.4 was written by
xnox_canonical <dimitri.ledkov@canonical.com> in 2014.
Source: https://codereview.appspot.com/104960043/

Rebased against Go 1.6.2 by Boris Nagaev <bnagaev@gmail.com>.

diff --git a/src/cmd/dist/build.go b/src/cmd/dist/build.go
index 1111111..2222222 100644
--- a/src/cmd/dist/build.go
+++ b/src/cmd/dist/build.go
@@ -41,6 +41,7 @@ var (
 	defaultldflags   string
 	defaultcxxtarget string
 	defaultcctarget  string
+	defaultpkgconfigtarget  string
 	rebuildall       bool
 	defaultclang     bool
 
@@ -203,6 +204,12 @@ func xinit() {
 	}
 	defaultcxxtarget = b
 
+	b = os.Getenv("PKG_CONFIG")
+	if b == "" {
+		b = "pkg-config"
+	}
+	defaultpkgconfigtarget = b
+
 	// For tools being invoked but also for os.ExpandEnv.
 	os.Setenv("GO386", go386)
 	os.Setenv("GOARCH", goarch)
diff --git a/src/cmd/dist/buildgo.go b/src/cmd/dist/buildgo.go
index 1111111..2222222 100644
--- a/src/cmd/dist/buildgo.go
+++ b/src/cmd/dist/buildgo.go
@@ -15,6 +15,7 @@ import "fmt"
 //	package main
 //	const defaultCC = <defaultcc>
 //	const defaultCXX = <defaultcxx>
+//	const defaultPkgConfig = <defaultpkgconfig>
 //
 // It is invoked to write cmd/go/zdefaultcc.go
 // but we also write cmd/cgo/zdefaultcc.go
@@ -27,8 +28,9 @@ func mkzdefaultcc(dir, file string) {
 			"package main\n"+
 			"\n"+
 			"const defaultCC = `%s`\n"+
-			"const defaultCXX = `%s`\n",
-		defaultcctarget, defaultcxxtarget)
+			"const defaultCXX = `%s`\n"+
+			"const defaultPkgConfig = `%s`\n",
+		defaultcctarget, defaultcxxtarget, defaultpkgconfigtarget)
 
 	writefile(out, file, writeSkipSame)
 
diff --git a/src/cmd/go/build.go b/src/cmd/go/build.go
index 1111111..2222222 100644
--- a/src/cmd/go/build.go
+++ b/src/cmd/go/build.go
@@ -1575,13 +1575,19 @@ func (b *builder) build(a *action) (err error) {
 	return nil
 }
 
+// pkgconfigCmd returns a pkg-config binary name
+// defaultPkgConfig is defined in zdefaultcc.go, written by cmd/dist.
+func (b *builder) pkgconfigCmd() string {
+   return envList("PKG_CONFIG", defaultPkgConfig)[0]
+}
+
 // Calls pkg-config if needed and returns the cflags/ldflags needed to build the package.
 func (b *builder) getPkgConfigFlags(p *Package) (cflags, ldflags []string, err error) {
 	if pkgs := p.CgoPkgConfig; len(pkgs) > 0 {
 		var out []byte
-		out, err = b.runOut(p.Dir, p.ImportPath, nil, "pkg-config", "--cflags", pkgs)
+		out, err = b.runOut(p.Dir, p.ImportPath, nil, b.pkgconfigCmd(), "--cflags", pkgs)
 		if err != nil {
-			b.showOutput(p.Dir, "pkg-config --cflags "+strings.Join(pkgs, " "), string(out))
+			b.showOutput(p.Dir, b.pkgconfigCmd()+" --cflags "+strings.Join(pkgs, " "), string(out))
 			b.print(err.Error() + "\n")
 			err = errPrintedOutput
 			return
@@ -1589,9 +1595,9 @@ func (b *builder) getPkgConfigFlags(p *Package) (cflags, ldflags []string, err e
 		if len(out) > 0 {
 			cflags = strings.Fields(string(out))
 		}
-		out, err = b.runOut(p.Dir, p.ImportPath, nil, "pkg-config", "--libs", pkgs)
+		out, err = b.runOut(p.Dir, p.ImportPath, nil, b.pkgconfigCmd(), "--libs", pkgs)
 		if err != nil {
-			b.showOutput(p.Dir, "pkg-config --libs "+strings.Join(pkgs, " "), string(out))
+			b.showOutput(p.Dir, b.pkgconfigCmd()+" --libs "+strings.Join(pkgs, " "), string(out))
 			b.print(err.Error() + "\n")
 			err = errPrintedOutput
 			return