[DebugInfo][InstrRef] Preserve properties of restored variables

[DebugInfo][InstrRef] Preserve properties of restored variables

InstrRefBasedLDV observes when variable locations are clobbered, scans what
values are available in the machine, and re-issues a DBG_VALUE for the
variable if it can find another location. Unfortunately, I hadn't joined up
the Indirectness flag, so if it did this to an Indirect Value, the
indirectness would be dropped.

Fix this, and add a test that if we clobber a variable value (on the stack
in this case), then the recovered variable location keeps the Indirect
flag.

Differential Revision: https://reviews.llvm.org/D114378