What’s your setup? MSBuild – which is the standard way to build Windows projects – takes care of paths itself. You should probably stick to it whenever possible.
VS provides no other automatic way to set up environment – you have to search for the necessary .bat, (or a shortcut to it in the Start menu) yourself, and they are often broken.
As can be seen from a snapshot of a Windows builder directory structure, there are a bunch of vcvars*.bat lying around – as said earlier, it’s up to you to find the needed one and hope that it works.
You cannot import envvars from a .bat directly into the running shell 'cuz Travis uses Git Bash as the shell which cannot source .bats, obviously.
But you can invoke something like
MSYS2_ARG_CONV_EXCL="*" cmd /c call <path\to\bat> \&\& nmake
(You’ll have to find the necessary quoting and escaping by trial and error. Try with a local Git Bash for faster turnaround.)