Don't allow multiple line entries with the same address to exist sequentially.

The compiler, when JIT'ing code, can emit illegal DWARF line tables (address is line table sequences must increase). This changes fixes that issue by replacing previous line entries whose start address is the same with the new line entry to avoid having multiple line entries with the same address. Since the address range of lines entries is determined by the delta between the current and next line entry, this shouldn't cause any issues.