go/build, cmd/go: add support for .syso files

.syso files are system objects copied directly
into the package archive.

Fixes #1552.

R=alex.brainman, iant, r, minux.ma, remyoudompheng
CC=golang-dev
https://golang.org/cl/5778043

src/cmd/go/build.go

@@ -727,6 +727,11 @@ func (b *builder) build(a *action) error {
 	// http://golang.org/issue/2601
 	objects = append(objects, cgoObjects...)
 
+	// Add system object files.
+	for _, syso := range a.p.SysoFiles {
+		objects = append(objects, filepath.Join(a.p.Dir, syso))
+	}
+
 	// Pack into archive in obj directory
 	if err := buildToolchain.pack(b, a.p, obj, a.objpkg, objects); err != nil {
 		return err

src/cmd/go/list.go

@@ -46,6 +46,7 @@ being passed to the template is:
         CFiles   []string  // .c source files
         HFiles   []string  // .h source files
         SFiles   []string  // .s source files
+        SysoFiles []string // .syso object files to add to archive
 
         // Cgo directives
         CgoCFLAGS    []string // cgo: flags for C compiler

src/cmd/go/pkg.go

@@ -40,6 +40,7 @@ type Package struct {
 	CFiles    []string `json:",omitempty"` // .c source files
 	HFiles    []string `json:",omitempty"` // .h source files
 	SFiles    []string `json:",omitempty"` // .s source files
+	SysoFiles []string `json:",omitempty"` // .syso system object files added to package
 
 	// Cgo directives
 	CgoCFLAGS    []string `json:",omitempty"` // cgo: flags for C compiler
@@ -90,6 +91,7 @@ func (p *Package) copyBuild(pp *build.Package) {
 	p.CFiles = pp.CFiles
 	p.HFiles = pp.HFiles
 	p.SFiles = pp.SFiles
+	p.SysoFiles = pp.SysoFiles
 	p.CgoCFLAGS = pp.CgoCFLAGS
 	p.CgoLDFLAGS = pp.CgoLDFLAGS
 	p.CgoPkgConfig = pp.CgoPkgConfig
@@ -487,7 +489,7 @@ func isStale(p *Package, topRoot map[string]bool) bool {
 		return false
 	}
 
-	srcs := stringList(p.GoFiles, p.CFiles, p.HFiles, p.SFiles, p.CgoFiles)
+	srcs := stringList(p.GoFiles, p.CFiles, p.HFiles, p.SFiles, p.CgoFiles, p.SysoFiles)
 	for _, src := range srcs {
 		if olderThan(filepath.Join(p.Dir, src)) {
 			return true

src/pkg/go/build/build.go

@@ -284,6 +284,7 @@ type Package struct {
 	CFiles    []string // .c source files
 	HFiles    []string // .h source files
 	SFiles    []string // .s source files
+	SysoFiles []string // .syso system object files to add to archive
 
 	// Cgo directives
 	CgoPkgConfig []string // Cgo pkg-config directives
@@ -476,7 +477,12 @@ Found:
 		ext := name[i:]
 		switch ext {
 		case ".go", ".c", ".s", ".h", ".S":
-			// tentatively okay
+			// tentatively okay - read to make sure
+		case ".syso":
+			// binary objects to add to package archive
+			// Likely of the form foo_windows.syso, but
+			// the name was vetted above with goodOSArchFile.
+			p.SysoFiles = append(p.SysoFiles, name)
 		default:
 			// skip
 			continue