error: 'constexpr' does not name a type m- arduino ide

I'm trying to compile this C++ code using the Arduino 1.0.5-r2 IDE

#include <cstdint>
#include "mcal_reg.h"

class led
{
public:
  // Use convenient class-specific typedefs.
  typedef std::uint8_t port_type;
  typedef std::uint8_t bval_type;

  // The led class constructor.
  led(const port_type p,
      const bval_type b) : port(p),
                           bval(b)
  {
    // Set the port pin to low.
    *reinterpret_cast<volatile bval_type*>(port)
      &= static_cast<bval_type>(~bval);

    // Set the port pin to output.
    *reinterpret_cast<volatile bval_type*>(port - 1U)
      |= bval;
  }

  void toggle() const
  {
    // Toggle the LED via direct memory access.
    *reinterpret_cast<volatile bval_type*>(port)
      ^= bval;
  }

private:
  // Private member variables of the class.
  const port_type port;
  const bval_type bval;
};

namespace
{
  // Create led_b5 on portb.5.
  const led led_b5
  {
    mcal::reg::portb,
    mcal::reg::bval5
  };
}

int main()
{
  // Toggle led_b5 in a loop forever.
  for(;;)
  {
    led_b5.toggle();
  }

And the include file mcal_reg.h is this:

  #ifndef _MCAL_REG_2011_11_04_H_
  #define _MCAL_REG_2011_11_04_H_

  #include <cstdint>

  namespace mcal
  {
    namespace reg
    {
      constexpr std::uint8_t portb = 0x25U;

      constexpr std::uint8_t bval0 = 0x01U;
      constexpr std::uint8_t bval1 = 0x01U << 1U;
      constexpr std::uint8_t bval2 = 0x01U << 2U;
      constexpr std::uint8_t bval3 = 0x01U << 3U;
      constexpr std::uint8_t bval4 = 0x01U << 4U;
      constexpr std::uint8_t bval5 = 0x01U << 5U;
      constexpr std::uint8_t bval6 = 0x01U << 6U;
      constexpr std::uint8_t bval7 = 0x01U << 7U;
    }
  }

#endif // _MCAL_REGISTERS_2011_11_04_H_

}

Trying to compile results in the following compilation error:

mcal_reg.h:17: error: 'constexpr' does not name a type

referring to this line: constexpr std::uint8_t portb = 0x25U;

I have setup a mcal_reg directory in my libraries folder which contains the mcal_reg.h file. This is my first Arduino project and I'm writing a program to be flashed to a standalone AVR chip. But I can't compile this program. My systems is Windows 7. and I only have the software that came with the Arduino IDE installed. (No separate GNU, Ms Visual Studio...etc) Please help.