If you don't make a library you'll have to:
1. add all cpp files in both projects, which will compile them n-times
2. add the .o files to the link additional linker options (I've never tried this because it is a hack), this approach is not recommended, because to get the proper setup you'll have to setup the correct external dependencies, so the project is correctly relinked if the .o files change.
If you don't want to bother with static lib go for solution 1. It is the easiest and safer approach. Then is your build starts to take too long, invest some time and separate the code in a static library.
If you go the number 2 route sooner or later you'll switch to number 1 or the static library.