[FPEnv] Update comment about nofpexcept default. NFC

[luke]

Summary

It no longer defaults to false as of 63336795f0d5

llvm/include/llvm/CodeGen/SelectionDAGNodes.h

private:
   bool AllowReciprocal : 1;
   bool AllowContract : 1;
   bool ApproximateFuncs : 1;
   bool AllowReassociation : 1;
 
   // We assume instructions do not raise floating-point exceptions by default,
   // and only those marked explicitly may do so.  We could choose to represent
   // this via a positive "FPExcept" flags like on the MI level, but having a
-  // negative "NoFPExcept" flag here (that defaults to true) makes the flag
-  // intersection logic more straightforward.
+  // negative "NoFPExcept" flag here makes the flag intersection logic more
+  // straightforward.
   bool NoFPExcept : 1;
   // Instructions with attached 'unpredictable' metadata on IR level.
   bool Unpredictable : 1;
 
 public:
   /// Default constructor turns off all optimization flags.
   SDNodeFlags()
       : NoUnsignedWrap(false), NoSignedWrap(false), Exact(false), NoNaNs(false),