[dwarfdump] Handle relocations in Dwarf accelerator tables

ELF targets (and maybe COFF) use relocations when referring
to strings in the .debug_str section. Handle that in the
accelerator table dumper. This commit restores the
test/DebugInfo/cross-cu-inlining.ll test to its expected
platform independant form, validating that the fix works
(this test failed on linux boxes).