Thanks for reporting this! When I compile on macOS Mojave 10.14.2 with the clang++ compiler, I also see the first warning you report above ("iqtensor.cc:428:26: warning: moving a temporary object prevents copy elision"), but I don't see the second warning. It may just be a difference in the compiler (different compilers will warn about different things).
We will look into making changes so these warnings don't appear, but for now you can likely just ignore them. If you want to check to make sure your installation is working properly, from your base ITensor directory, enter the unittest directory with `cd unittest` and type `make` to compile and run all of the tests. If all of the tests compile and pass, your installation of ITensor is working correctly! Another good test is to enter the sample directory from your base ITensor directory with `cd sample` and type `make`, and then run the sample DMRG runs with commands like `./dmrg`. This is a good test that the DMRG code in ITensor is working correctly.