Portage is possible only for OpenSource code, ClosedSource can only be run using Emu, Wine on GNU/Linux or other VM …
Each portage is different, my experience tell you that using opensource technologies is the best way to do this.
From Windows .Net projects , mono could be a nice alternative, but I am usure about MicroSoft specific ApI
From Windows C++ code, compiling with GcC under WindowS (using ming or cygwin) could be a 1st acchievement, it should be easly (in the oposite direction you'll figure out that MsvC miss many feature or the standards).
MSVC based projects must be “translated” to other build system, Let me suggest to use cmake, since it could be used backward to build the win32 project.
Real hackers will try to translate msvc projects files (xml) to CMakeFiles.txt using XSLT.
Common issues easy to fix :