Fix a whitespace regression in MIR printing that was introduced in
https://github.com/llvm/llvm-project/pull/137361.

The default value for `ListSeparator` is `", "`, so we don't need to
print an additional space in front of tokens for optional symbols and
other things printed after operands.

Note, the modified LIT test will fail at trunk without the fix,
demonstrating that the extra space before `, pre-instr-symbol <mcsymbol
>` on Line 63 exists currently and is fixed with this change.

This patch adds the MIR parsing and serialization support for save and
restore points with subsets of callee saved registers. That is, it
syntactically allows a function to contain two or more distinct
sub-regions in which distinct subsets of registers are spilled/filled as
callee save. This is useful if e.g. one of the CSRs isn't modified in
one of the sub-regions, but is in the other(s).

Support for actually using this capability in code generation is still
forthcoming. This patch is the next logical step for multiple
save/restore points support.

All points are now stored in DenseMap from MBB to vector of
CalleeSavedInfo.

Shrink-Wrap points split Part 4.
RFC:
https://discourse.llvm.org/t/shrink-wrap-save-restore-points-splitting/83581

Part 1: https://github.com/llvm/llvm-project/pull/117862 (landed)
Part 2: https://github.com/llvm/llvm-project/pull/119355 (landed)
Part 3: https://github.com/llvm/llvm-project/pull/119357 (landed)
Part 5: https://github.com/llvm/llvm-project/pull/119359 (likely to be
further split)

Remove the type alias now that the std::variant aspect is gone, directly
using std::vector in the few places that need it is more idiomatic.

Move a routine from a core header to single user.

In review of bbde6b, I had originally proposed that we support the
legacy text format. As review evolved, it bacame clear this had been a
bad idea (too much complexity), but in order to let that patch finally
move forward, I approved the change with the variant. This change undoes
the variant, and updates all the tests to just use the array form.

Currently mir supports only one save and one restore point
specification:

```
  savePoint:       '%bb.1'
  restorePoint:    '%bb.2'
```

This patch provide possibility to have multiple save and multiple
restore points in mir:

```
  savePoints:
    - point:           '%bb.1'
  restorePoints:
    - point:           '%bb.2'
```

Shrink-Wrap points split Part 3.
RFC:
https://discourse.llvm.org/t/shrink-wrap-save-restore-points-splitting/83581

Part 1: https://github.com/llvm/llvm-project/pull/117862
Part 2: https://github.com/llvm/llvm-project/pull/119355
Part 4: https://github.com/llvm/llvm-project/pull/119358
Part 5: https://github.com/llvm/llvm-project/pull/119359

This flag applies to G_PTR_ADD instructions and indicates that the operation
implements an inbounds getelementptr operation, i.e., the pointer operand is in
bounds wrt. the allocated object it is based on, and the arithmetic does not
change that.

It is set when the IRTranslator lowers inbounds GEPs (currently only in some
cases, to be extended with a future PR), and in the
(build|materialize)ObjectPtrOffset functions.

Inbounds information is useful in ISel when we have instructions that perform
address computations whose intermediate steps must be in the same memory region
as the final result. A follow-up patch will start using it for AMDGPU's flat
memory instructions, where the immediate offset must not affect the memory
aperture of the address.

This is analogous to a concurrent effort in SDAG: #131862
(related: #140017, #141725).

For SWDEV-516125.

This reverts commit 05e08cdb3e576cc0887d1507ebd2f756460c7db7.
Adding the missing -mtriple flags in MIR/X86 test files which caused
these tests to fail which was the reason for reverting the patch.

If the update_mir_test_checks.py script is aware of MIFlags, it can produce
meaningful identifiers in generated FileCheck lines. A few MIFlags that were
introduced more recently have been missing from the script.

Ideally, the MIFlags would be specified in a single place and automatically
made known to the script to avoid this divergence, but for now adding a comment
pointing to the script at the place where the MIFlags are printed seems like a
reasonable trade-off.

This PR only regenerates check lines for a single test as an example of the
effect; other affected tests are not regenerated for now to avoid unnecessary
test churn.