Flutter iOS post-clone script does not build with right XCode version

[alexli1st]

The appcenter-post-clone script for Flutter iOS build starts the build right away after cloning Flutter SDK and running flutter doctor, before AppCenter runs the script that sets the XCode path based on user's build configuration. As a result, flutter is always building against the default XCode version instead of user's selected XCode version.

One way that fixed the issue for me is to remove the line "flutter build iOS --release --no-codesign" from the appcenter-post-clone.sh script and add a appcenter-pre-build.sh script to include the following:

#!/usr/bin/env bash
set -e
set -x
cd ..
export PATH=pwd/flutter/bin:$PATH
flutter build ios --release --no-codesign

[dipree]

@AlexLi1984 please feel free to update the existing script in a PR.