[DebugInfo] Change to constructor homing debug info mode: skip literal types

Summary:
In constructor type homing mode sometimes complete debug info for constexpr
types was missing, because there was not a constructor emitted. This change
makes constructor type homing ignore constexpr types.

Reviewers: rnk, dblaikie

Subscribers: aprantl, cfe-commits

Tags: #clang

Differential Revision: https://reviews.llvm.org/D77432