Fix C++ Macro Usages when Definition contains Newline.

Now truncates the displayed line at the first Newline character after
the Macro name.

Task-number: QTCREATORBUG-7113

Change-Id: Ifb13c01d10b97098b54ac4346a80f0dcff3a35f3
Reviewed-by: Orgad Shaneh <orgads@gmail.com>
Reviewed-by: Erik Verbruggen <erik.verbruggen@nokia.com>