This is a speculative fix for tail call frame support on Linux.
Logs provided by @stella.stamenova indicate that on Linux, lldb adds a spurious slide offset to the return PC it loads from AT_call_return_pc attributes (see the list thread: "[PATCH] D50478: Add support for artificial tail call frames").
This patch side-steps the issue by getting rid of the load address calculation in lldb's CallEdge::GetReturnPCAddress.
The idea is to have the DWARF writer emit function-local offsets to the instruction after a call. I.e. return-pc = label-after-call-insn - function-entry. LLDB can simply add this offset to the base address of a function to get the return PC.
I'm open to other ideas here. I've tested that this works on Darwin, but not on Linux.