Add the running contexts to the config system.

def SetPlatformArchContext():
  """Add the running contexts to the config system."""

  # Initialize the running platform context:
  _CONFIG.AddContext("Platform:%s" % platform.system().title())

  machine = platform.uname()[4]
  if machine in ["x86_64", "AMD64", "i686"]:
    # 32 bit binaries running on AMD64 will still have a i386 arch.
    if platform.architecture()[0] == "32bit":
      arch = "i386"
    else:
      arch = "amd64"
  elif machine == "x86":
    arch = "i386"
  else:
    arch = machine

  _CONFIG.AddContext("Arch:%s" % arch)