Fix the build for git repositories with multiple remotes.

Summary:
When a git repository had multiple remotes, ${repository} will be set to a multiline string. This causes compilation errors in SVNVersion.inc.

Fix this by limiting the output of utils/GetRepositoryPath to the first remote (which is reasonably likely to be 'origin').

Reviewers: jordan_rose

CC: llvm-commits, t.p.northover

Differential Revision: http://llvm-reviews.chandlerc.com/D1659