This is a step towards eliminating the vestigial second operand of
DBG_VALUE, which is always an immediate zero or noreg and only indicates
if the debug value is indirect in memory. Today, the offset is carried
in the DIExpression, and soon the indirection will live there too.
Many of the test case updates remove DW_OP_deref to better match the IR
that clang generates after r300523, which removed DW_OP_deref from VLAs
and indirect parameters.