Based on the list discussion from the other day, this does the following:
- Moves Dwarf.h, ELF.h, COFF.h, Wasm.h, MachO.h, all corresponding .def files, and all xxxReloc folders out of Support and into ObjectLayout.
- Moves the file_magic structure and identify_magic functions from Support to ObjectLayout.
- Moves corresponding unit tests from SupportTests to a new unit test target named ObjectLayoutTests.
- Updates all relevant LLVMBuild.txt files.
- Updates all code in llvm, clang, lld, and lldb to use the new header locations.
Sorry this patch is so large, but there is really no good way around it.