[globalisel][irtranslator] Verify that DILocations aren't lost in translation

Summary:
Also fix a couple bugs where DILocations are lost. EntryBuilder wasn't passing
on debug locations for PHI's, constants, GLOBAL_VALUE, etc.

Reviewers: aprantl, vsk, bogner, aditya_nandakumar, volkan, rtereshin, aemerson

Reviewed By: aemerson

Subscribers: aemerson, rovka, kristof.beyls, javed.absar, llvm-commits

Differential Revision: https://reviews.llvm.org/D53740

llvm-svn: 345743