NOISSUE block MS account adding on macOS < 10.13 builds

It's never going to work with Qt 5.6, so there's no point.
People need to update.

launcher/pages/global/AccountListPage.cpp

@@ -128,6 +128,18 @@ void AccountListPage::on_actionAddMojang_triggered()
 
 void AccountListPage::on_actionAddMicrosoft_triggered()
 {
+    if(BuildConfig.BUILD_PLATFORM == "osx64") {
+        CustomMessageBox::selectable(
+            this,
+            tr("Microsoft Accounts not available"),
+            tr(
+                "Microsoft accounts are only usable on macOS 10.13 or newer, with fully updated MultiMC.\n\n"
+                "Please update both your operating system and MultiMC."
+            ),
+            QMessageBox::Warning
+        )->exec();
+        return;
+    }
     MinecraftAccountPtr account = MSALoginDialog::newAccount(
         this,
         tr("Please enter your Mojang account email and password to add your account.")