In 4 years the ELF debugger support plugin wasn't adapted to other
object formats or debugging approaches. After the renaming NFC in
https://github.com/llvm/llvm-project/pull/168343, this patch tailors the
plugin to ELF and section load-address patching. It allows removal of
abstractions and consolidate processing steps with the newly enabled
AllocActions from https://github.com/llvm/llvm-project/pull/168343.
The key change is to process debug sections in one place in a
post-allocation pass. Since we can handle the endianness of the ELF file
the single `visitSectionLoadAddresses()` visitor function now, we don't
need to track debug objects and sections in template classes anymore. We
keep using the `DebugObject` class and drop `DebugObjectSection`,
`ELFDebugObjectSection<ELFT>` and `ELFDebugObject`.
Furthermore, we now use the allocation's working memory for load-address
fixups directly. We can drop the `WritableMemoryBuffer` from the debug
object and most of the `finalizeWorkingMemory()` step, which saves one
copy of the entire debug object buffer. Inlining `finalizeAsync()` into
the pre-fixup pass simplifies quite some logic.
We still track `RegisteredObjs` here, because we want to free memory
once the corresponding code is freed. There will be a follow-up patch
that turns it into a dealloc action.
In 4 years the plugin wasn't adapted to other object formats. This patch
makes it specific for ELF, which will allow to remove some abstractions
down the line. It also moves the plugin from LLVMOrcJIT into
LLVMOrcDebugging, which didn't exist back then.
