cmd/link/internal/ld: make dwarf_test and associated testdata module-agnostic

Updates #30228

Change-Id: I31aac4cb113c0c88a54329181ad27aee3d8acc71
Reviewed-on: https://go-review.googlesource.com/c/162835
Run-TryBot: Bryan C. Mills <bcmills@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Than McIntosh <thanm@google.com>

src/cmd/link/internal/ld/dwarf_test.go

@@ -114,26 +114,14 @@ func gobuild(t *testing.T, dir string, testfile string, gcflags string) *builtFi
 	return &builtFile{f, dst}
 }
 
-func envWithGoPathSet(gp string) []string {
-	env := os.Environ()
-	for i := 0; i < len(env); i++ {
-		if strings.HasPrefix(env[i], "GOPATH=") {
-			env[i] = "GOPATH=" + gp
-			return env
-		}
-	}
-	env = append(env, "GOPATH="+gp)
-	return env
-}
+// Similar to gobuild() above, but uses a main package instead of a test.go file.
 
-// Similar to gobuild() above, but runs off a separate GOPATH environment
-
-func gobuildTestdata(t *testing.T, tdir string, gopathdir string, packtobuild string, gcflags string) *builtFile {
+func gobuildTestdata(t *testing.T, tdir string, pkgDir string, gcflags string) *builtFile {
 	dst := filepath.Join(tdir, "out.exe")
 
 	// Run a build with an updated GOPATH
-	cmd := exec.Command(testenv.GoToolPath(t), "build", gcflags, "-o", dst, packtobuild)
-	cmd.Env = envWithGoPathSet(gopathdir)
+	cmd := exec.Command(testenv.GoToolPath(t), "build", gcflags, "-o", dst)
+	cmd.Dir = pkgDir
 	if b, err := cmd.CombinedOutput(); err != nil {
 		t.Logf("build: %s\n", b)
 		t.Fatalf("build error: %v", err)
@@ -727,7 +715,7 @@ func main() {
 	}
 }
 
-func abstractOriginSanity(t *testing.T, gopathdir string, flags string) {
+func abstractOriginSanity(t *testing.T, pkgDir string, flags string) {
 	t.Parallel()
 
 	dir, err := ioutil.TempDir("", "TestAbstractOriginSanity")
@@ -737,7 +725,7 @@ func abstractOriginSanity(t *testing.T, gopathdir string, flags string) {
 	defer os.RemoveAll(dir)
 
 	// Build with inlining, to exercise DWARF inlining support.
-	f := gobuildTestdata(t, dir, gopathdir, "main", flags)
+	f := gobuildTestdata(t, dir, filepath.Join(pkgDir, "main"), flags)
 
 	d, err := f.DWARF()
 	if err != nil {

src/cmd/link/internal/ld/testdata/issue25459/main/main.go

@@ -1,6 +1,6 @@
 package main
 
-import "a"
+import "cmd/link/internal/ld/testdata/issue25459/a"
 
 var Glob int
 

src/cmd/link/internal/ld/testdata/issue26237/main/main.go

@@ -3,7 +3,7 @@ package main
 import (
 	"fmt"
 
-	b "b.dir"
+	b "cmd/link/internal/ld/testdata/issue26237/b.dir"
 )
 
 var skyx int