Although the wasm-linker previously already supported
debug information in incremental-mode, this was no longer
working as-is with the addition of supporting object-file-parsed
debug information. This commit implements the Zig-created debug information
structure from scratch which is a lot more robust and also allows
being linked with debug information from other object files.
When linking a Zig-compilation with an object file,
we allow mixing the debug atoms to make sure debug
information is preserved from object files. By default,
we now always initialize all debug sections if the `strip` flag
is unset.
This also fixes relocations for debug information as previously
the offset of an atom wasn't calculated, and neither was the code
size itself which meant that debug lines were off and file names
from other object files were missing.
Previously we used single arraylists for each debug section for debug
information that was generated from Zig code. (e.i. `Module` is available).
This information is now stored in Atoms, similarly to debug information
from object files. This will allow us to link them together and resolve
debug relocations.
This correctly performs a relocation for debug sections.
The result is that the wasm-linker can now correctly create
a binary from object files while preserving all debug information.
We now link relocatable debug sections with the correct
section symbol and then allocate and resolve the debug atoms
before writing them into the final binary.
Although this does perform the relocation, the actual relocations
are not done correctly yet.
Rather than storing the name of a debug section into the structure
`RelocatableData`, we use the `index` field as an offset into the
debug names table. This means we do not have to store an extra 16 bytes
for non-debug sections which can be massive for object files where each
data symbol has its own data section. The name of a debug section
can then be retrieved again when needed by using the offset and
then reading until the 0-delimiter.
Currently, `zig build-exe -fno-emit-bin --verbose-air src/main.zig`
results in no output at all. With this refactor, it dumps AIR
and then exits without invoking LLVM, as expected
