system mingw not recognized

Per the docs at
http://www.postgresql.org/docs/current/static/installation-platform-notes.html#INSTALLATION-NOTES-MINGW

"To build 64 bit binaries using MinGW ... and run configure with the --host=x86_64-w64-mingw option"

But when I try to run:  $ ~/sources/postgresql-9.5.0/configure --host=x86_64-w64-mingw

I get an error system mingw not recognized:

checking build system type... x86_64-pc-mingw64
checking host system type... Invalid configuration `x86_64-w64-mingw': system `mingw' not recognized
configure: error: /bin/sh /home/Admin/sources/postgresql-9.5.0/config/config.sub x86_64-w64-mingw failed

The sources were downloaded from http://www.postgresql.org/ftp/source/v9.5.0/

Are the docs up to date?

Thanks