Initialize the default value of SymbolFileDWARF uuid with
the appropriately shifted DW_INVALID_OFFSET constant.
This change fixes the collision in the computation of DIE uid
(inside DIERef::GetUID) and incorrect CompileUnit lookup
(because of the misleading cu_offset value).
Test plan: make check-lldb
Differential revision: https://reviews.llvm.org/D42563
llvm-svn: 323832