llvm::CallBase::getArgOperand returns Value *, so we do not need
const_cast<Value *>.

This is for consistency with #139401.

This reverts commit 534d221b63bb52f64e1f3ad3c40cfb87323d28ec.

The initial patch (#135782 caused issues because it emits an error, and llc is sensitive to it.
It also caused compiler-rt/lib/scudo/standalone/tests/wrappers_cpp_test.cpp to fail.

Use warnings instead + reject lowering. That way, the fallback path is used without llc/clang returning a failure code.
If fallback isn't enabled then the warnings provide context as to why lowering failed.

Original commit description for #135782:

Instead of printing something to dbgs (which is not visible to all users),
emit a diagnostic like the DAG does. We still crash later because we fail to
select the inline assembly, but at least now users will know why it's crashing.

In a future patch we could also recover from the error like the DAG does, so the
lowering can keep going until it either crashes or gives a different error later.

This reverts commit c22081c320340d0e7542b247ee093ca515509b52.

Instead of printing something to dbgs (which is not visible to all users),
emit a diagnostic like the DAG does. We still crash later because we fail to
select the inline assembly, but at least now users will know why it's crashing.

In a future patch we could also recover from the error like the DAG does, so the
lowering can keep going until it either crashes or gives a different error later.

Similar to https://github.com/llvm/llvm-project/pull/96902, this adds
`getDataLayout()` helpers to Function and GlobalValue, replacing the
current `getParent()->getDataLayout()` pattern.

We have an internal test affected by
https://github.com/llvm/llvm-project/commit/a69673615bb9f14794056470a32f70f60a52213d.
The reason is we haven't modeled rounding control registers for inline
asm under constraint FP.
Here is a reduced case:  https://godbolt.org/z/s4EsKP94e

[GlobalISel] Implement convergence control tokens and intrinsics in GMIR

In the IR translator, convert the LLVM token type to LLT::token(), which is an
alias for the s0 type. These show up as implicit uses on convergent operations.

Differential Revision: https://reviews.llvm.org/D158147

Given a list of constraints for InlineAsm (ex. "imr") I'm looking to
modify the order in which they are chosen. Before doing so, I noticed a
fair
amount of logic is duplicated between SelectionDAGISel and GlobalISel
for this.

That is because SelectionDAGISel is also trying to lower immediates
during selection. If we detangle these concerns into:
1. choose the preferred constraint
2. attempt to lower that constraint

Then we can slide down the list of constraints until we find one that
can be lowered. That allows the implementation to be shared between
instruction selection frameworks.

This makes it so that later I might only need to adjust the priority of
constraints in one place, and have both selectors behave the same.