This is to fix #115710.

Just insert addrspacecast in cases where the alloca uses a
different address space, since I don't know what else you
could possibly do.

This adds the `llvm.sincos` intrinsic, legalization, and lowering.

The `llvm.sincos` intrinsic takes a floating-point value and returns
both the sine and cosine (as a struct).

```
declare { float, float }          @llvm.sincos.f32(float  %Val)
declare { double, double }        @llvm.sincos.f64(double %Val)
declare { x86_fp80, x86_fp80 }    @llvm.sincos.f80(x86_fp80  %Val)
declare { fp128, fp128 }          @llvm.sincos.f128(fp128 %Val)
declare { ppc_fp128, ppc_fp128 }  @llvm.sincos.ppcf128(ppc_fp128  %Val)
declare { <4 x float>, <4 x float> } @llvm.sincos.v4f32(<4 x float>  %Val)
```

The lowering is built on top of the existing FSINCOS ISD node, with
additional type legalization to allow for f16, f128, and vector values.

This change is part of this proposal:
https://discourse.llvm.org/t/rfc-all-the-math-intrinsics/78294

Based on example PR #96222 and fix PR #101268, with some differences due
to 2-arg intrinsic and intermediate refactor (RuntimeLibCalls.cpp).

- Add llvm.experimental.constrained.atan2 - Intrinsics.td,
ConstrainedOps.def, LangRef.rst
- Add to ISDOpcodes.h and TargetSelectionDAG.td, connect to intrinsic in
BasicTTIImpl.h, and LibFunc_ in SelectionDAGBuilder.cpp
- Update LegalizeDAG.cpp, LegalizeFloatTypes.cpp, LegalizeVectorOps.cpp,
and LegalizeVectorTypes.cpp
- Update isKnownNeverNaN in SelectionDAG.cpp
- Update SelectionDAGDumper.cpp
- Update libcalls - RuntimeLibcalls.def, RuntimeLibcalls.cpp
- TargetLoweringBase.cpp - Expand for vectors, promote f16
- X86ISelLowering.cpp - Expand f80, promote f32 to f64 for MSVC

Part 4 for Implement the atan2 HLSL Function #70096.

When lowering `FSINCOS` to a library call (that takes output pointers)
we can avoid creating new stack allocations if the results of the
`FSINCOS` are being stored. Instead, we can take the destination
pointers from the stores and pass those to the library call.

---

Note: As a NFC this also adds (and uses) `RTLIB::getFSINCOS()`.

This reverts commit ababfee78714313a0cad87591b819f0944b90d09.

Add X86 FP80 check.

Reverts llvm/llvm-project#109116