Partially revert r111155. It looks like MSVC is calling an operator<() that
clang says is unused.

llvm-svn: 111167
diff --git a/llvm/lib/Target/X86/X86FloatingPoint.cpp b/llvm/lib/Target/X86/X86FloatingPoint.cpp
index f597f47..4bf7cdb 100644
--- a/llvm/lib/Target/X86/X86FloatingPoint.cpp
+++ b/llvm/lib/Target/X86/X86FloatingPoint.cpp
@@ -572,6 +572,9 @@
     friend bool operator<(const TableEntry &TE, unsigned V) {
       return TE.from < V;
     }
+    friend bool operator<(unsigned V, const TableEntry &TE) {
+      return V < TE.from;
+    }
   };
 }