- Extract RelocScan to RelocScan.h. The file includes Target.h, and
cannot be merged with Relocations.h
- Add MIPS and PPC64 specific relocation scanners, removing runtime
checks for other targets.

This refactoring prepares the codebase for better target-specific
optimizations and easier addition of target-specific behavior.

relocateAlloc can be called with either InputSection (including
SyntheticSection like GotSection) or EhInputSection.

Introduce relocateEh so that we can remove some boilerplate and replace
relocateAlloc's parameter type with `InputSection`.

Pull Request: https://github.com/llvm/llvm-project/pull/160031

This ensures subsequent calls to elf::postScanRelocations with a new Ctx
will correctly use an instance with the right internalFile (with the old
one presumably deleted, even). It also avoids having to create a new
instance in elf::getErrorPlace, and will allow more uses of such a dummy
symbol in future commits.

Reviewers: MaskRay

Reviewed By: MaskRay

Pull Request: https://github.com/llvm/llvm-project/pull/150796

and simplify `+ toStr(ctx, x)` to `<< x`.
The trailing '\n' << llvm::getBugReportMsg() is not very useful and
therefore removed.

so that we can remove the global `ctx` from toString implementations.
Rename lld::toString (to lld::elf::toStr) to simplify name lookup (we
have many llvm::toString and another lld::toString(const llvm::opt::Arg
&)).

The current diagnostic functions log/warn/error/fatal lack a context
argument and call the global `lld::errorHandler()`, which prevents
multiple lld instances in one process.

This patch introduces context-aware replacements:

* log => Log(ctx)
* warn => Warn(ctx)
* errorOrWarn => Err(ctx)
* error => ErrAlways(ctx)
* fatal => Fatal(ctx)

Example: `errorOrWarn(toString(f) + "xxx")` => `Err(ctx) << f << "xxx"`.
(`toString(f)` is shortened to `f` as a bonus and may access `ctx`
without accessing the global variable (see `Target.cpp`)).

`ctx.e = &context->e;` can be replaced with a non-global Errorhandler
when `ctx` becomes a local variable.

(For the ELF port, the long term goal is to eliminate `error`. Most can
be straightforwardly converted to `Err(ctx)`.)