Add a FIXME.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@131108 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Frontend/InitPreprocessor.cpp

@@ -343,6 +343,7 @@ static void InitializePredefinedMacros(const TargetInfo &TI,
       // Since we define wchar_t in C++ mode.
       Builder.defineMacro("_WCHAR_T_DEFINED");
       Builder.defineMacro("_NATIVE_WCHAR_T_DEFINED");
+      // FIXME: Support Microsoft's __identifier extension in the lexer.
       Builder.append("#define __identifier(x) x");
       Builder.append("class type_info;");
     }