Teach the explicit constructor check about constexpr.
Teach the explicit constructor check about constexpr.

If a constructor is marked constexpr it evades the explicit constructor
check right now, since the check only knows about the inline keyword.
Teach it that constexpr can be used also.

Change-Id: Ia76ddd00b69c5a76a385d22a2b9eb18b690bd8c8
Reviewed-on: https://chromium-review.googlesource.com/445932
Reviewed-by: Robbie Iannucci <40f3d43a28ebae3cb819288542e1c84d73d962d5@chromium.org>
Reviewed-by: Aaron Gable <bbed39beedae4cdb499af742d2fcd6c63934d93b@chromium.org>
Commit-Queue: Aaron Gable <bbed39beedae4cdb499af742d2fcd6c63934d93b@chromium.org>

CoherentLabs/depot_tools,CoherentLabs/depot_tools