circleci: Run bionic builds in a 32bit image

Closes #3702

.circleci/config.yml

@@ -196,7 +196,7 @@ jobs:
   distcheck:
     parameters:
       prefix:
-        description: the container image repository
+        description: the container image prefix (repository or architecture)
         type: string
         default: ""
       dist:
@@ -375,9 +375,9 @@ workflows:
           extra_conf: --enable-asan --enable-ubsan --enable-workspace-emulator
       - distcheck:
           name: distcheck_ubuntu_bionic
+          prefix: i386/
           dist: ubuntu
           release: bionic
-          extra_conf: CFLAGS='-g -O2 -m32'
       - distcheck:
           name: distcheck_alpine
           dist: alpine