How to sort mixed DWARF32 and DWARF64 .debug_*

[Fangrui Song]

I want to bring it to your attention that on llvm-dev some folks are discussing
how to sort mixed DWARF32 and DWARF64 .debug_* sections https://lists.llvm.org/pipermail/llvm-dev/2020-November/146522.html

There are merits placing DWARF32 .debug_info before DWARF64 .debug_info
because otherwise the DWARF32 .debug_info could still lead to out-of-range
relocations. This approach will however break the usual rule for linking
unrecognized sections:

   "When not otherwise constrained, sections should be emitted in input order."

https://lists.llvm.org/pipermail/llvm-dev/2020-November/146528.html
has an idea that DWARF64 sections can be detected by the relocation type (i.e.
on ppc64, check whether the first relocation is R_PPC64_ADDR64)