Directly call getIntrinsicID(), there is no need to check for
isIntrinsic() first.

Add per-property has<Prop>/set<Prop>/reset<Prop> functions to
MachineFunctionProperties.

getTgtMemIntrinsic should be able to propagate such information to the
MMO

I'm looking for ways to simplify the Mem*Inst class structure, and these
two seem to have fairly minimal justification, so let's remove them.

This is a reland of #138434 except that:

- the bits for llvm/lib/CodeGen/RenameIndependentSubregs.cpp
  have been dropped because they caused a test failure under asan, and

- the bits for llvm/lib/CodeGen/SelectionDAG/ScheduleDAGFast.cpp have
  been improved with structured bindings.

This reverts commit a9699a334bc9666570418a3bed9520bcdc21518b.

Breaks CodeGen/AMDGPU/collapse-endcf.ll in several configs
(sanitizer builds; macOS; possibly more), see comments on
https://github.com/llvm/llvm-project/pull/138434

This patch adds support for LLVM IR atomicrmw `fmaximum` and `fminimum`
instructions.

These mirror the `llvm.maximum.*` and `llvm.minimum.*` instructions, but
are atomic and use IEEE754 2019 handling for NaNs, which is different to
`fmax` and `fmin`. See:
     https://llvm.org/docs/LangRef.html#llvm-minimum-intrinsic
for more details.

Future changes will allow this LLVM IR to be lowered to specialised
assembler instructions on suitable targets, such as AArch64.