Try to drop the 'echo' hack.

appveyor.yml

@@ -30,7 +30,7 @@ build_script:
     # Run internal Hadrian tests
     - stack exec hadrian -- selftest
     # Build GHC
-    - echo "" | stack --no-terminal exec hadrian -- --lint --directory ".." -j --verbose --no-progress --progress-colour=never --profile=- --flavour=quickest
+    - stack exec hadrian -- --lint --directory ".." -j --verbose --no-progress --progress-colour=never --profile=- --flavour=quickest
     # Test GHC binary
     - cd ..
     - inplace\bin\ghc-stage2 -e 1+2