Fix regression of temporary_allocator with non-CUDA back ends
Fix regression of temporary_allocator with non-CUDA back ends

A recent cleanup of functions that have different code for host and device
accidentally broke temporary_allocator for non-CUDA back ends.  An #if
condition that protects a piece of code that only works with the CUDA back
end was incorrectly removed.  This fix adds that condition back in.

jaredhoberock/thrust,jaredhoberock/thrust,jaredhoberock/thrust,andrewcorrigan/thrust-multi-permutation-iterator,thrust/thrust,thrust/thrust,jaredhoberock/thrust,thrust/thrust,andrewcorrigan/thrust-multi-permutation-iterator,andrewcorrigan/thrust-multi-permutation-iterator,jaredhoberock/thrust,thrust/thrust,thrust/thrust