Expose nvcc --objdir-as-tempdir?

[timrlaw]

Hi,

I was wondering if there was any appetite for exposing nvcc's --objdir-as-tempdir option as an AMReX CMake option. We'd quite like to use this option in our project, as the default puts things in /tmp which is open to clashes between users compiling the same code on a shared node, and also liable to fill up /tmp as nvcc doesn't always clean up when Ctrl-C'ing builds.

It would seem cleanest to add this option at the AMReX level so it is applied consistently across the whole code.

I've made an accompanying PR that implements this.