Experiment with specifying Arm resource class

There are a few different ways to cross compile glibc, this way uses
CircleCI's resource classes which are available for using Arm with
"Remote Docker": https://circleci.com/docs/using-docker/#arm

.circleci/config.yml

@@ -5,7 +5,7 @@ executors:
       - image: docker:git
     environment:
       GLIBC_VERSION: 2.39
-    resource_class: large
+    resource_class: arm.large
     working_directory: ~/docker-glibc-builder
   artefact-uploader:
     docker: