Installing DeSmuME from source on Windows
Since all of the Windows developers make use of Microsoft Visual Studio, only that compiler is supported on Windows.
All dependencies are included in the source code download. The only things you are required to install is a supported compiler, and (when checking out SVN), a SVN client.
Install Microsoft Visual Studio Community 2015
For a Windows build, you first have to download and install Microsoft Visual Studio Community 2015 (which is free). Download the web or ISO installer from the links at https://stackoverflow.com/questions/44290672/how-to-download-visual-studio-community-edition-2015-not-2017#answer-44290942
Change the installation type to Custom and next. Now make sure you select open up Programming Languages > Visual C++ and select "Common Tools for Visual C++ 2015" and "Windows XP Support for C++". The latter option adds significant size, but it's what desmume is using. Now you can unclick "Windows and Web Development".
To be clear, this should leave only the two items mentioned above being installed.
From there you can proceed with the installation and you'll have what you need.
Retrieving the sources
There are 2 ways you can get the code.
Go to https://sourceforge.net/p/desmume/code/HEAD/tree/ and select “Download Snapshot”. Due to sourceforge sucking, this may take 1 million years and never finish successfully.
Download it and open with your archive manager (if you haven’t one, I suggest 7zip at http://www.7-zip.org/).
Inside there is another one archive, open it and you’ll see the source code.
Extract into a folder of your choice. Now are you ready to compile.
The main advantage here is you don’t need the SVN client, the disadvantage is that every time a new SVN is released you need to download again the entire source tarball.
Get code with Git client
You can follow guides which you can find anywhere online for how to clone a git repository. But for some reason we chose to write another guide here. This one may not be great.
Go to http://tortoisesvn.net/downloads, download TortoiseGIT, install it then reboot. Now create a folder where the code will be downloaded (ex. D:\Desmume\source). Right click on it and select “TortoiseGit->Clone...”
Enter https://github.com/TASVideos/desmume.git for the URL, then press OK
Wait until TortoiseGit has downloaded all the source files then press OK.
Now you’re ready to compile.
The main advantage here is that TortoiseGit will download only the modified files when you check for a new Git version, the disadvantage is that the first time take a while to download all the code. When you want to update the source code you only need to do “TortoiseGit->Pull and click OK”.
Compile your SVN
In "desmume/src/windows" open DeSmuME.sln
Then Visual Studio should open up. Change "Debug" to "Release" where you can readily see it on the screen and then press CTRL+ALT+F7.
After the compile completes, the executable should be located in "desmume/src/windows/__bins/DeSmuME-VS2015-Release.exe".
If your system can't support Visual Studio 2015, you can use Visual C++ Express 2010 instead. Microsoft has hidden it so you can use this direct URL: http://download.microsoft.com/download/1/D/9/1D9A6C0E-FC89-43EE-9658-B9F0E3A76983/vc_web.exe . From there, you'll have to improvise. The steps are very similar to what's above. Use DeSmuME_2010.bat instead of DeSmuME.sln, however.