re PR go/77910 (go: open zversion.go: no such file or directory)

PR go/77910
    cmd/go: don't check standard packages when using gccgo
    
    This copies https://golang.org/cl/33295 to libgo.
    
    This fixes GCC PR 77910.
    
    Reviewed-on: https://go-review.googlesource.com/33471

From-SVN: r242724

gcc/go/gofrontend/MERGE

@@ -1,4 +1,4 @@
-7593cc83a03999331c5e2dc65a9306c5fe57dfd0
+e66f30e862cb5d02b9d55bf44ac439bb8fc4ea19
 
 The first line of this file holds the git revision number of the last
 merge done from the gofrontend repository.

libgo/go/cmd/go/pkg.go

@@ -523,6 +523,11 @@ func disallowInternal(srcDir string, p *Package, stk *importStack) *Package {
 		return p
 	}
 
+	// We can't check standard packages with gccgo.
+	if buildContext.Compiler == "gccgo" && p.Standard {
+		return p
+	}
+
 	// The stack includes p.ImportPath.
 	// If that's the only thing on the stack, we started
 	// with a name given on the command line, not an
@@ -1588,7 +1593,7 @@ func computeBuildID(p *Package) {
 	// Include the content of runtime/internal/sys/zversion.go in the hash
 	// for package runtime. This will give package runtime a
 	// different build ID in each Go release.
-	if p.Standard && p.ImportPath == "runtime/internal/sys" {
+	if p.Standard && p.ImportPath == "runtime/internal/sys" && buildContext.Compiler != "gccgo" {
 		data, err := ioutil.ReadFile(filepath.Join(p.Dir, "zversion.go"))
 		if err != nil {
 			fatalf("go: %s", err)