cmd/go: fix addition of "math" dependency for arm binaries

p.ImportPath is the directory-derived path (like cmd/go).
p.Name is the actual package name.

Fixes #12089.

Change-Id: Ief76d42a85f811b0dfe2218affb48551527a7d44
Reviewed-on: https://go-review.googlesource.com/13530Reviewed-by: David Crawshaw <crawshaw@golang.org>

src/cmd/go/go_test.go

@@ -2352,3 +2352,23 @@ func TestGoBuildOutput(t *testing.T) {
 	tg.runFail("build", "-o", "whatever", "cmd/gofmt", "sync/atomic")
 	tg.grepStderr("multiple packages", "did not reject -o with multiple packages")
 }
+
+func TestGoBuildARM(t *testing.T) {
+	if testing.Short() {
+		t.Skip("skipping cross-compile in short mode")
+	}
+
+	tg := testgo(t)
+	defer tg.cleanup()
+
+	tg.makeTempdir()
+	tg.cd(tg.path("."))
+
+	tg.setenv("GOARCH", "arm")
+	tg.setenv("GOOS", "linux")
+	tg.setenv("GOARM", "5")
+	tg.tempFile("hello.go", `package main
+		func main() {}`)
+	tg.run("build", "hello.go")
+	tg.grepStderrNot("unable to find math.a", "did not build math.a correctly")
+}

src/cmd/go/pkg.go

@@ -836,7 +836,7 @@ func (p *Package) load(stk *importStack, bp *build.Package, err error) *Package
 			importPaths = append(importPaths, "runtime/race")
 		}
 		// On ARM with GOARM=5, everything depends on math for the link.
-		if p.ImportPath == "main" && goarch == "arm" {
+		if p.Name == "main" && goarch == "arm" {
 			importPaths = append(importPaths, "math")
 		}
 	}