[DebugInfo][InstrRef] Add extra indirection for NRVO tests
In some scenarios, usually involving NRVO, we can issue indirect DBG_VALUEs
after SelectionDAG, even in instruction referencing mode (if the variable
is an argument). If the corresponding argument value is spilt to the stack,
then we have:
- Indirection from it being on the stack,
- Indirection from it being a dbg.declare or a dbg.addr.
However InstrRefBasedLDV only emits one level of indirection. This patch
adds the second, by adding an extra DW_OP_deref if necessary. The two
tests modified fail otherwise -- they feature some NRVO, and require two
levels of indirection to be correct.
Differential Revision: https://reviews.llvm.org/D114364