[LLD][ELF] - Improve the DWARF v5 suport for building .gdb_index.

Now LLD might build the broken/incomplete .gdb_index when some DWARF v5
sections (like .debug_rnglists and .debug_addr) are used.

Particularly, for the case above, we emit an empty address area. 
A test case is provided and patch fixes the issue.

Differential revision: https://reviews.llvm.org/D55109

llvm-svn: 348119