Maybe I don't understand correctly what do you mean, I'm not sure about the
(I don't usually touch the environment settings) although I did do a bunch of updates recently
.
Do you mean that you update the config of C::B, the config of your project (if yes, only one target -debug | release- or all?) or the source of your project?
If it's about the code, then sometimes I have problem close to yours.
In those cases, I clean the project in all it's targets, then rebuild.
When after that there still is a problem, the compiler/linker output (if you have enabled the full log) give some clues to find what is it.