Remove a FIXME, the driver handles -O4.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@68481 91177308-0d34-0410-b5e6-96231b3b80d8

tools/clang-cc/clang-cc.cpp

@@ -617,7 +617,6 @@ struct OptLevelParser : public llvm::cl::parser<unsigned> {
              const std::string &Arg, unsigned &Val) {
     if (llvm::cl::parser<unsigned>::parse(O, ArgName, Arg, Val))
       return true;
-    // FIXME: Support -O4.
     if (Val > 3)
       return O.error(": '" + Arg + "' invalid optimization level!");
     return false;