[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).

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@222029 91177308-0d34-0410-b5e6-96231b3b80d8