The normal object file on Windows has a limit of `2^16`
sections that can be in an object-file.
The `big-obj` format raises this to `2^32` sections.
The implementation is made difficult because we now need to support
two header formats and two section formats that differ only by a single
element size within each. The element that's different is in the middle
of the structs and since the structs are used to map regions of memory
directly, it means we need to know which struct it is when we do the
mapping or pointer arithmetics.
This is the final Object-Code format which Windows compilers can generate
which we do not support yet in GHCI. All other major compilers on the platforms
can produce it and all linkers consume it (bfd and lld).
This patch abstracts away retrieving the fields to functions which all take
an struct which describes which object format is currently being parsed.
These functions are always in-lined as they're small but would looks messy
being copy-pasted everywhere.