[Clang-CL] Teach clang-cl about /constexpr cl switches

[Neumann-A]

cl switches

/constexpr:depth<N>
/constexpr:backtrace<N>
/constexpr:steps<N>

just need to be mapped to:

  -fconstexpr-backtrace-limit=<value>
                          Set the maximum number of entries to print in a constexpr evaluation backtrace (0 = no limit)
  -fconstexpr-depth=<value>
                          Set the maximum depth of recursive constexpr function calls
  -fconstexpr-steps=<value>
                          Set the maximum number of steps in constexpr function evaluation