cmd/go: avoid repeated include dirs.

Fixes #3171.

R=golang-dev, rsc
CC=golang-dev, remy
https://golang.org/cl/5724045

diff --git a/src/cmd/go/build.go b/src/cmd/go/build.go
index d14278acbc44a4cb1b893b4d15062d2d0b3acbdf..382f61e89b14c65ec6b66a6bcf116fbf7ca628d3 100644 (file)
--- a/src/cmd/go/build.go
+++ b/src/cmd/go/build.go
@@ -790,12 +790,12 @@ func (b *builder) includeArgs(flag string, all []*action) []string {
        // Finally, look in the installed package directories for each action.
        for _, a1 := range all {
                if dir := a1.pkgdir; dir == a1.p.build.PkgRoot && !incMap[dir] {
+                       incMap[dir] = true
                        if _, ok := buildToolchain.(gccgoToolchain); ok {
                                dir = filepath.Join(dir, "gccgo")
                        } else {
                                dir = filepath.Join(dir, goos+"_"+goarch)
                        }
-                       incMap[dir] = true
                        inc = append(inc, flag, dir)
                }
        }