Add a note that people shouldn't use MachineFunctionInfo.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@15823 91177308-0d34-0410-b5e6-96231b3b80d8

lib/CodeGen/MachineFunction.cpp

@@ -309,6 +309,8 @@ void MachineConstantPool::dump() const { print(std::cerr); }
 
 //===----------------------------------------------------------------------===//
 //  MachineFunctionInfo implementation
+//  NOTE: MachineFunctionInfo and its methods are specific to the SparcV9
+//  target - don't use them in other targets.
 //===----------------------------------------------------------------------===//
 
 static unsigned