Fix build dependency if swig wrapper and documentation is both switched on

[libftdi] / README.mingw

* How to cross compile libftdi-1.x for Windows? *
   1 - Prepare a pkg-config wrapper according to
       https://www.flameeyes.eu/autotools-mythbuster/pkgconfig/cross-compiling.html ,
       additionally export PKG_CONFIG_ALLOW_SYSTEM_CFLAGS and
       PKG_CONFIG_ALLOW_SYSTEM_LIBS.
   2 - Write a CMake toolchain file according to
       http://www.vtk.org/Wiki/CmakeMingw . Change the path to your future sysroot.
   3 - Get libusb sources (either by cloning the git repo or by downloading a
       tarball). Unpack, autogen.sh (when building from git), and configure like this:
       ./configure --build=`./config.guess` --host=i686-w64-mingw32 \
               --prefix=/usr --with-sysroot=$HOME/i686-w64-mingw32-root/
   4 - run
       make install DESTDIR=$HOME/i686-w64-mingw32-root/
   5 - go to libftdi-1.x source directory and run
       cmake -DCMAKE_TOOLCHAIN_FILE=~/Toolchain-mingw.cmake \
             -DCMAKE_INSTALL_PREFIX="/usr" \
             -DPKG_CONFIG_EXECUTABLE=`which i686-w64-mingw32-pkg-config`
   6 - run
       make install DESTDIR=$HOME/i686-w64-mingw32-root/

* How to run libftdi 1.x under Windows *

On 26-Jan-2014, libusbx and libusb project were merged with the release
of libusb-1.0.18 and now the project is called libusb.

libusb Windows backend will need to rely on a proper driver to run.
Please refer to the following wiki page for proper driver installation.
https://github.com/libusb/libusb/wiki/Windows#wiki-How_to_use_libusb_on_Windows

As of 26-Jan-2014, libusb Windows backend supports WinUSB,
libusb0.sys and libusbk.sys driver. However, libusb's support of
libusb0.sys and libusbk.sys is considered to be less mature than
WinUSB. Therefore, WinUSB driver installation using Zadig
is recommended.

Take note once you replace the original FTDI driver with WinUSB driver,
you can no longer use the functionality the original FTDI driver provides
(eg. Virtual Serial Port or D2XX).