Do not clean the Xcode build folder if the action specifies 'clean_bu…

[rapidsna]

…ild' to be 'false'

Without this fix, GIT command cleaned the build folder even if the
action specified 'clean_build' to be 'false'. This fix allows an
individual action to skip clean when 'clean_build' is explicitly
set 'false'.

Pull Request Description

Replace with a description of this pull request. Instructions for adding
projects are available in the README.

Acceptance Criteria

To be accepted into the Swift source compatibility test suite, a project must:

• be an Xcode or swift package manager project
• support building on either Linux or macOS
• target Linux, macOS, or iOS/tvOS/watchOS device
• be contained in a publicly accessible git repository
• maintain a project branch that builds against Swift 4.0 and passes any unit tests
• have maintainers who will commit to resolve issues in a timely manner
• be compatible with the latest GM/Beta versions of Xcode and swiftpm
• add value not already included in the suite
• be licensed with one of the following permissive licenses:
  • BSD
  • MIT
  • Apache License, version 2.0
  • Eclipse Public License
  • Mozilla Public License (MPL) 1.1
  • MPL 2.0
  • CDDL
• pass ./project_precommit_check script run

Ensure project meets all listed requirements before submitting a pull request.

[rapidsna]

@swift-ci please test

[clackary]

LGTM!

[rapidsna]

Thanks @clackary @shahmishal for reviewing!! swift-ci tests failed but the failures don't seem to be related to this change. How do you want me to proceed with this?