[llvm] [X86][GlobalISel] Support fp80 for G_FPTRUNC and G_FPEXT (PR #141611)

[Matt Arsenault via llvm-commits]

================
@@ -8410,6 +8412,33 @@ LegalizerHelper::lowerFPTOINT_SAT(MachineInstr &MI) {
   return Legalized;
 }
 
+// fp conversions using truncating and extending loads and stores.
----------------
arsenm wrote:

```suggestion
// Floating-point conversions using truncating and extending loads and stores.
```

https://github.com/llvm/llvm-project/pull/141611