[llvm] [SDAG] Add missing SoftenFloatRes legalization for FMODF (PR #129264)

[Björn Pettersson via llvm-commits]

bjope wrote:

This isn't fully working for our downstream target.

Our targets calling convention is using different registers for pointers and integers. But the pointer argument will end up being treated as an integer argument. Now we get
```
  t127: ch,glue = CopyToReg t126, Register:i16 $integer_register_0, FrameIndex:i16<0>, t126:1, t1.c:49:9
  t129: ch,glue = MyTarget::CALL t127, TargetExternalSymbol:i16'modf', Register:i16 $integer_register_0, t127:1, t1.c:49:9
```
while the correct thing would be
```
  t127: ch,glue = CopyToReg t126, Register:i16 $pointer_register_0, FrameIndex:i16<0>, t126:1, t1.c:49:9
  t129: ch,glue = MyTarget::CALL t127, TargetExternalSymbol:i16'modf', Register:i16 $pointer_register_0, t127:1, t1.c:49:9
```

As far as I can tell other libcalls involving pointers (e.g. looking at SelectionDAG::getMemset, or SelectionDAG::expandMultipleResultFPLibCall) is using LowerCallTo directly without using the makeLibCall helper. The TargetLowering::makeLibCall helper does not support setting setting Entry.Ty to identify a PointerType when setting up the ArgListTy vector.

https://github.com/llvm/llvm-project/pull/129264