[llvm] [NVPTX] Support copysign PTX instruction (PR #107800)

[Pranav Kant via llvm-commits]

pranavk wrote:

@AlexMaclean I have this I can share:

```
LLVM ERROR: Cannot select: t31: f32 = fcopysign ConstantFP:f32<5.000000e-01>, t17
  t19: f32 = ConstantFP<5.000000e-01>
  t17: f16,ch = load<(invariant load (s16) from %ir.7, addrspace 1)> t0, t16, undef:i64
    t16: i64 = add t10, t34
      t10: i64 = addrspacecast[0 -> 1] t35
        t35: i64,ch = load<(dereferenceable invariant load (s64) from `ptr addrspace(101) null`, addrspace 101)> t0, TargetExternalSymbol:i64'foo', undef:i64
          t1: i64 = TargetExternalSymbol'foo'
          t3: i64 = undef
      t34: i64 = NVPTXISD::MUL_WIDE_UNSIGNED t12, Constant:i32<2>
        t12: i32 = llvm.nvvm.read.ptx.sreg.tid.x TargetConstant:i64<8487>
          t11: i64 = TargetConstant<8487>
        t33: i32 = Constant<2>
    t3: i64 = undef
```

I will be working on getting the LLVM IR for you unless above is sufficient. Please let me know.


https://github.com/llvm/llvm-project/pull/107800