[GNC-dev] Windows master build

[Robert Fewell]

Guys,
Tried to do a build on my Windows 10 setup after doing some updates to OS
and build system and it failed for these reasons...

CMakeLists.txt , line 927 and 928 could not find the dll's specified
Changing find_library to find_file worked, this maybe due to cmake being
updated to 3.17.0

Also it failed on inno setup, gnucash_mingw64.iss, line 135, libffi-6.dll
is now libffi-7.dll

Not sure if the build server does a msys/mingw update on a regular basis,
thought I would point out what happened to me.

Regards,
Bob