LLVM currently represents floating-point negation as -0.0 - x. Fix

FastISel to recognize this pattern and emit a floating-point
negation using xor.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@80963 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/CodeGen/FastISel.h

@@ -300,6 +300,8 @@ protected:
 private:
   bool SelectBinaryOp(User *I, ISD::NodeType ISDOpcode);
 
+  bool SelectFNeg(User *I);
+
   bool SelectGetElementPtr(User *I);
 
   bool SelectCall(User *I);