Firstly, this is old code that I inherited and I would love to clean it up and make it perfect someday, but I cannot do that today. Therefore, I ask that answers like "rewrite the whole thing so that there are no circular dependencies" not be given.
I have a solution with 44 projects. Most of the projects build DLLs and a few build executables. There are multiple projects that depend on another project that, in one way or another, requires the first. Some are as simple as A requires B.lib and B requires A.lib and others are longer chains that loop back around.
When I inherited the code, it was not clean and there were old build files still amongst the source, namely .LIB files. Without removing those .LIB files all 44 projects are able to build and all of the old .LIB files are replaced with newly built files. This tells me that if I build a second time, none of the old .LIBs are being used and that all of my deliverables are now entirely generated from current source.
This leaves me with a problem: I wanted to clean out all none source files from version control, but if I do so, then I can no longer build the projects.
To further clearify, the projects that build DLLs create a .LIB file as an intermidiate step and these files are copied into a common folder that is listed in the "Additional Library Directories" property of each project and the individual .LIB files that are needed for a give project are in the "Additional Dependencies" property for that project.
Edit: I am not looking to do a major overhaul of the code. I know that all of the object files that all of the projects need are created. I also know that this structure is not optimal. I do, however, believe that if the linker knew where to look, it could find everything that is needed.
Extract just the parts from A that B requires into a new DLL 'C'. Then make both A depend on both B & C, whereas B just depends on C.
It's not going to be easy, but just keep extracting little bits at a time.