[clang-format] Replace IncompleteFormat by a struct with Line

Summary: This patch replaces the boolean IncompleteFormat that is used to notify the client if an unrecoverable syntax error occurred by a struct that also contains a line number.

Reviewers: djasper

Reviewed By: djasper

Subscribers: cfe-commits, klimek

Differential Revision: https://reviews.llvm.org/D32298

llvm-svn: 300985