Identified with misc-include-cleaner.

... matching what we have in the disassembler. This isn't turned on by
default since several of the scheduling models are not completely
accurate, and we don't want to be misleading.

getOperandLatency has the following behavior: it returns -1 as a special
value, negative numbers other than -1 on some target-specific overrides,
or a valid non-negative latency. This behavior can be surprising, as
some callers do arithmetic on these negative values. Change the
interface of getOperandLatency to return a std::optional<unsigned> to
prevent surprises in callers. While at it, change the interface of
getInstrLatency to return unsigned instead of int.

This change was inspired by a refactoring in
TargetSchedModel::computeOperandLatency.

I also ran `git clang-format` to get the headers in the right order for
the new location, which has changed the order of other headers in two
files.

Some extra minor cleanup.

Discourse thread: https://discourse.llvm.org/t/include-what-you-use-include-cleanup
Differential Revision: https://reviews.llvm.org/D121329

This moves the registry higher in the LLVM library dependency stack.
Every client of the target registry needs to link against MC anyway to
actually use the target, so we might as well move this out of Support.

This allows us to ensure that Support doesn't have includes from MC/*.

Differential Revision: https://reviews.llvm.org/D111454

This makes it possible for targets to define their own MCObjectFileInfo.
This MCObjectFileInfo is then used to determine things like section alignment.

This is a follow up to D101462 and prepares for the RISCV backend defining the
text section alignment depending on the enabled extensions.

Reviewed By: MaskRay

Differential Revision: https://reviews.llvm.org/D101921

This untangles the MCContext and the MCObjectFileInfo. There is a circular
dependency between MCContext and MCObjectFileInfo. Currently this dependency
also exists during construction: You can't contruct a MOFI without a MCContext
without constructing the MCContext with a dummy version of that MOFI first.
This removes this dependency during construction. In a perfect world,
MCObjectFileInfo wouldn't depend on MCContext at all, but only be stored in the
MCContext, like other MC information. This is future work.

This also shifts/adds more information to the MCContext making it more
available to the different targets. Namely:

- TargetTriple
- ObjectFileType
- SubtargetInfo

Reviewed By: MaskRay

Differential Revision: https://reviews.llvm.org/D101462

The argument is llvm::null() everywhere except llvm::errs() in
llvm-objdump in -DLLVM_ENABLE_ASSERTIONS=On builds. It is used by no
target but X86 in -DLLVM_ENABLE_ASSERTIONS=On builds.

If we ever have the needs to add verbose log to disassemblers, we can
record log with a member function, instead of passing it around as an
argument.