Microsoft have released a free version of Visual Studio, which includes MFC these days. So it is now easy to recompile MUSHclient.
You can get it from https://www.visualstudio.com/free which redirects to https://www.visualstudio.com/products/free-developer-offers-vs.
Choose the Visual Studio Community download:

The is a small installer program. When run you can choose what you want. I went for Custom and I selected the following items:

Note that you need around 18 GB of disk to install.
After installing you can grab a copy of the MUSHclient source from https://github.com/nickgammon/mushclient
Personally I would install Git and use that to get the source, because then you can get updates in the future. Using the Git command line, go to a suitable directory and enter:
Alternatively you could download the .zip file with this link:
https://github.com/nickgammon/mushclient/archive/master.zip
After opening Visual Studio you should be able to open the "solution" file in the MUSHclient source folder.
Then build the solution and you should get an error-free compile (maybe with a warning or two).
For testing you need various other files which are normally in the MUSHclient release distribution, such as lua5.1.dll, and the resources file which is in the "locale" directory.
The easiest way to test would be to copy the MUSHclient.exe file from the build (in the Windebug directory) into an existing MUSHclient download. That way all the support files and folders are in the right place.
If you got the source using Git, when new versions are released, you can get them by using the Git "shell" and typing:
You can get it from https://www.visualstudio.com/free which redirects to https://www.visualstudio.com/products/free-developer-offers-vs.
Choose the Visual Studio Community download:

The is a small installer program. When run you can choose what you want. I went for Custom and I selected the following items:

Note that you need around 18 GB of disk to install.
After installing you can grab a copy of the MUSHclient source from https://github.com/nickgammon/mushclient
Personally I would install Git and use that to get the source, because then you can get updates in the future. Using the Git command line, go to a suitable directory and enter:
Alternatively you could download the .zip file with this link:
https://github.com/nickgammon/mushclient/archive/master.zip
After opening Visual Studio you should be able to open the "solution" file in the MUSHclient source folder.
Then build the solution and you should get an error-free compile (maybe with a warning or two).
For testing you need various other files which are normally in the MUSHclient release distribution, such as lua5.1.dll, and the resources file which is in the "locale" directory.
The easiest way to test would be to copy the MUSHclient.exe file from the build (in the Windebug directory) into an existing MUSHclient download. That way all the support files and folders are in the right place.
If you got the source using Git, when new versions are released, you can get them by using the Git "shell" and typing:
git fetch
git merge origin/master