Moved GlobList into a separate header file

Summary:
It is a separate abstraction that is used in more contexts than just
a helper for ClangTidyDiagnosticConsumer.

Subscribers: mgorny, cfe-commits

Tags: #clang

Differential Revision: https://reviews.llvm.org/D66747

llvm-svn: 369918
GitOrigin-RevId: a6fed93f0d1077f24e83fcd8abd31443acaf80e6