Somme error / help message refer to options with a single dash while
help refer to options with a double dash.

The new round-robin algorithm overrides the hash-based distribution of
functions to modules. It achieves a more even number of functions per
module when the number of functions is close to the number of requested
modules. It's not in use by default and is available under a new flag.

Should fix the ASAN error.

Allow targets to implement custom module splitting logic for
--lto-partitions, see #89245

https://discourse.llvm.org/t/rfc-lto-target-specific-module-splittting/77252

The cleanup was manual, but assisted by "include-what-you-use". It consists in

1. Removing unused forward declaration. No impact expected.
2. Removing unused headers in .cpp files. No impact expected.
3. Removing unused headers in .h files. This removes implicit dependencies and
   is generally considered a good thing, but this may break downstream builds.
   I've updated llvm, clang, lld, lldb and mlir deps, and included a list of the
   modification in the second part of the commit.
4. Replacing header inclusion by forward declaration. This has the same impact
   as 3.

Notable changes:

- llvm/Support/TargetParser.h no longer includes llvm/Support/AArch64TargetParser.h nor llvm/Support/ARMTargetParser.h
- llvm/Support/TypeSize.h no longer includes llvm/Support/WithColor.h
- llvm/Support/YAMLTraits.h no longer includes llvm/Support/Regex.h
- llvm/ADT/SmallVector.h no longer includes llvm/Support/MemAlloc.h nor llvm/Support/ErrorHandling.h

You may need to add some of these headers in your compilation units, if needs be.

As an hint to the impact of the cleanup, running

clang++ -E  -Iinclude -I../llvm/include ../llvm/lib/Support/*.cpp -std=c++14 -fno-rtti -fno-exceptions | wc -l

before: 8000919 lines
after:  7917500 lines

Reduced dependencies also helps incremental rebuilds and is more ccache
friendly, something not shown by the above metric :-)

Discourse thread on the topic: https://llvm.discourse.group/t/include-what-you-use-include-cleanup/5831

Differential Revision: https://reviews.llvm.org/D106430

splitCodeGen does not need to take ownership of the module, as it
currently clones the original module for each split operation.

There is an ~4 year old fixme to change that, but until this is
addressed, the function can just take a reference to the module.

This makes the transition of LTOCodeGenerator to use LTOBackend a bit
easier, because under some circumstances, LTOCodeGenerator needs to
write the original module back after codegen.

Reviewed By: tejohnson

Differential Revision: https://reviews.llvm.org/D95222

verifyFunction/verifyModule don't assert or error internally. They
also don't print anything if you don't pass a raw_ostream to them.
So the caller needs to check the result and ideally pass a stream
to get the messages. Otherwise they're just really expensive no-ops.

I've filed PR45965 for another instance in SLPVectorizer
that causes a lit test failure.

Differential Revision: https://reviews.llvm.org/D80106

F_{None,Text,Append} are kept for compatibility since r334221.

llvm-svn: 367800

to reflect the new license.

We understand that people may be surprised that we're moving the header
entirely to discuss the new license. We checked this carefully with the
Foundation's lawyer and we believe this is the correct approach.

Essentially, all code in the project is now made available by the LLVM
project under our new license, so you will see that the license headers
include that license only. Some of our contributors have contributed
code under our old license, and accordingly, we have retained a copy of
our old license notice in the top-level files in each project and
repository.

llvm-svn: 351636