[llvm/DebugInfo] Emit DW_OP_implicit_value when tuning for LLDB

This patch enables emitting DWARF `DW_OP_implicit_value` opcode when
tuning debug information for LLDB (`-debugger-tune=lldb`).

This will also propagate to Darwin platforms, since they use LLDB tuning
as a default.

rdar://67406059

Differential Revision: https://reviews.llvm.org/D90001



Signed-off-by: Med Ismail Bennani <medismail.bennani@gmail.com>