This patch (8/N) stems from D69787
Summary: Just invoked salvaging debug info function before deleting the instructions. Testing: - Added unit tests for validation of LLVM IR and object file thru llvm-dwarfdump - check-llvm, and an end-to-end test using gnu GDB to debug an optimized program (LLDB need to be enhanced to support). - check-debuginfo (the debug info integration tests)