Because 7-zip doesn't have a public repository, and their code is released only as archives on SourceForge, I maintain a git-ified copy here.
The tagged releases and the original branch contain pure 7-zip releases, without any modifications like this readme.
start with "VS2015 x86 Native Tools Command Prompt" / "VS2015 x64 Native Tools Command Prompt"
cd CPP\7zip\UI\FileManager
nmake
use prebuild 7zFm.exe[x86] to overwrite C:\Program Files (x86)\7-Zip\7zFM.exe
use prebuild 7zFm.exe[x64] to overwrite C:\Program Files\7-Zip\7zFM.exe
extract 7z920_extra.7z to get 7zxa.dll, and then overwrite 7zxa.dll to C:\Program Files (x86)\Beyond Compare 3\7zxa.dll