[PATCH] Use -std=c++11 when no arguments are provided.

[Guillaume Papin]

  Can I suggest using `getNumOccurrences()` once again?

    if (BuildPath.getNumOccurrences() > 0)
      // -p specified
    else
      // -p not specified

  http://llvm.org/docs/doxygen/html/classllvm_1_1cl_1_1Option.html#add4bb5355441c007e7ed0e374f221040

http://llvm-reviews.chandlerc.com/D1337