[llvm] [ARM] Remove `UnsafeFPMath` uses (PR #151275)

[Matt Arsenault via llvm-commits]

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@@ -186,6 +186,9 @@ class ARMSubtarget : public ARMGenSubtargetInfo {
   /// IsLittle - The target is Little Endian
   bool IsLittle;
 
+  /// DM - Denormal mode
+  DenormalMode DM;
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arsenm wrote:

Should comment why this is here 

https://github.com/llvm/llvm-project/pull/151275