Validate missing imports in CI (#127)

Author: Lukasa

docker/docker-compose.2004.main.yaml

@@ -10,7 +10,8 @@ services:
 
   test:
     image: swift-crypto:20.04-main
-    environment: []
+    environment:
+      - IMPORT_CHECK_ARG=--explicit-target-dependency-import-check error
       #- SANITIZER_ARG=--sanitize=thread
 
   cmake:

docker/docker-compose.yaml

@@ -29,8 +29,8 @@ services:
   test:
     <<: *common
     # FIXME: get rid of existing warnings
-    #command: /bin/bash -xcl "swift test --enable-test-discovery -Xswiftc -warnings-as-errors $${SANITIZER_ARG-}"
-    command: /bin/bash -xcl "swift test --enable-test-discovery"
+    #command: /bin/bash -xcl "swift test --enable-test-discovery -Xswiftc -warnings-as-errors $${SANITIZER_ARG-} $${IMPORT_CHECK_ARG-}"
+    command: /bin/bash -xcl "swift test --enable-test-discovery $${IMPORT_CHECK_ARG-}"
 
   cmake:
     <<: *common