Extract mixins from compat layer conditionals

• Type: Bug
• Status: Closed
• Resolution: Fixed
• Affects Version/s: Master
• Fix Version/s: 7.1.0 M2, 7.1.X, Master
• Component/s: Themes Infrastructure > Compatibility Layer
• Labels: None
• Git Pull Request: https://github.com/brianchandotcom/liferay-portal/pull/56236

To avoid SCSS errors