Re-land "Fix faulty assertion in debug info"

This had been reverted because the new test failed on non-X86 bots.  I moved
the new test to the appropriate subdirectory to correct this.

Differential Revision: https://reviews.llvm.org/D41264
Original submission:  r321122 (which was reverted by r321125)

This reverts commit 3c1639b5703c387a0d8cba2862803b4e68dff436.

llvm-svn: 321911