Include first KDECompilerSettings, so all other included macros pick up cmake policies

Summary:
From cmake_policy() documentation:
"Functions and macros record policy settings when they are created and use
the pre-record policies when they are invoked."

As KDECompilerSettings sets at least CMP0063, it needs to be included before
all other files which define macros affected by this policy, like ECMAddTests.

Reviewers: apol, mwolff, kfunk

Reviewed By: apol, kfunk

Subscribers: kdevelop-devel

Differential Revision: https://phabricator.kde.org/D2896