Support compiling with CMAKE_BUILD_TYPE set to None (#405)
Support compiling with CMAKE_BUILD_TYPE set to None (#405)

Debian defaults to setting CMAKE_BUILD_TYPE to None and setting CFLAGS
and alike to Debian standards.
damonkohler/cartographer,cartographer-project/cartographer,cartographer-project/cartographer,googlecartographer/cartographer,cartographer-project/cartographer,wohe/cartographer,larics/cartographer,wohe/cartographer,wohe/cartographer,googlecartographer/cartographer,cartographer-project/cartographer,larics/cartographer,larics/cartographer,googlecartographer/cartographer,damonkohler/cartographer,damonkohler/cartographer,wohe/cartographer,damonkohler/cartographer,larics/cartographer,googlecartographer/cartographer