cmake: Give descriptive error to user when cloned with core.autocrlf

Windows users have on multiple occasions cloned Zephyr using a Windows
git client. It seems that the windows git client defaults to
converting line endings from LF to CRLF when cloning repo's. This
breaks at least one of Zephyr's tools (Kconfig).

This patch introduces a sanity check of the environment for MSYS
users.

Signed-off-by: Sebastian Bøe <sebastian.boe@nordicsemi.no>