Memoize PHP compatibility info
Summary: Ref T7892. Avoid reading the PHP compatibility information for every file being linted.
Test Plan:
Before
real 1m24.327s user 1m19.571s sys 0m5.239s
real 1m12.029s user 1m5.756s sys 0m5.502s
Reviewers: epriestley, Blessed Reviewers
Reviewed By: epriestley, Blessed Reviewers
Subscribers: Korvin, epriestley
Maniphest Tasks: T7892
Differential Revision: https://secure.phabricator.com/D12518