[clang-tidy][NFC] Tweak GlobList to iterate backwards

By iterating backwards over the globs we can exit the loop as soon as we find a match.

While we're here:
 - Regex doesn't need to be mutable.
 - We can reserve the amount of Globs needed ahead of time.
 - Using a SmallVector with size 0 is slightly more space efficient than a std::vector.

Reviewed By: aaron.ballman

Differential Revision: https://reviews.llvm.org/D91033