py-fiona @1.7.11.post1 do not build with gdal 2.3

[dmarteau (David Marteau)]

Building py-fiona from source lead to the following error from gdal header:

/opt/local/include/cpl_port.h:187:6: error: Must have C++11 or newer.

This error is the same encountered when building fiona from source with pip without the compiler '-std=c++11' option. The current macport version of gdal is 2.3+ and require c++11: the actual configuration of py-fiona is not consistent with its dependencies.