Revert "Stop modifying upstream .gitignore file"

This reverts commit 049cf81.

As long as we are not yet changing the default build path, this should
be kept.

Author: guillemj

make.go

@@ -521,6 +521,29 @@ func createGitRepository(debsrc, gopkg, orig string, u *upstream,
 		return dir, fmt.Errorf("import-orig: %w", err)
 	}
 
+	{
+		f, err := os.OpenFile(filepath.Join(dir, ".gitignore"), os.O_APPEND|os.O_CREATE|os.O_WRONLY, 0644)
+		if err != nil {
+			return dir, fmt.Errorf("open .gitignore: %w", err)
+		}
+		// Beginning newline in case the file already exists and lacks a newline
+		// (not all editors enforce a newline at the end of the file):
+		if _, err := f.Write([]byte("\n/.pc/\n/_build/\n")); err != nil {
+			return dir, fmt.Errorf("write to .gitignore: %w", err)
+		}
+		if err := f.Close(); err != nil {
+			return dir, fmt.Errorf("close .gitignore: %w", err)
+		}
+	}
+
+	if err := runGitCommandIn(dir, "add", ".gitignore"); err != nil {
+		return dir, fmt.Errorf("git add .gitignore: %w", err)
+	}
+
+	if err := runGitCommandIn(dir, "commit", "-m", "Ignore _build and quilt .pc dirs via .gitignore"); err != nil {
+		return dir, fmt.Errorf("git commit (.gitignore): %w", err)
+	}
+
 	return dir, nil
 }