Fix build with glibmm-2.4 < 2.64 which lacks Glib::canonicalize_filename.
Use the underlying glib C function g_canonicalize_filename instead.
--- src/ui/dialog/export.cpp.orig
+++ src/ui/dialog/export.cpp
@@ -486,7 +486,13 @@
     }

     auto fname = Glib::build_filename(directory, Glib::filename_from_utf8(name));
-    return orig.empty() ? fname : Glib::canonicalize_filename(fname, orig);
+    if (orig.empty()) {
+        return fname;
+    }
+    auto *canonical = g_canonicalize_filename(fname.c_str(), orig.c_str());
+    std::string result(canonical);
+    g_free(canonical);
+    return result;
 }

 std::string Export::defaultFilename(SPDocument *doc, std::string &filename_entry_text, std::string extension)
--- src/ui/dialog/export-batch.cpp.orig
+++ src/ui/dialog/export-batch.cpp
@@ -540,7 +540,10 @@
     if (const char *doc_filename = _document->getDocumentFilename()) {
         auto doc_path = Glib::path_get_dirname(doc_filename);
         if (!path.empty()) {
-            return Glib::canonicalize_filename(path.raw(), doc_path);
+            auto *canonical = g_canonicalize_filename(path.raw().c_str(), doc_path.c_str());
+            std::string result(canonical);
+            g_free(canonical);
+            return result;
         }
         return doc_path;
     }