file(GET_RUNTIME_DEPENDENCIES): optimize on macOS

Calls to otool on macOS can be quite expensive, and due to repeated transitive libraries like those in Trilinos, CMake's GET_RUNTIME_DEPENDENCIES option makes numerous calls to resolve the same file's dependencies. This small addition memoizes the processed output from otool.

The following table demonstrates the 10x performance increase for a modern-cmake version of a subset of SCALE:

Version	otool calls	time	time w/ virus check
Original	1367	18.2s	22.4s
Optimized	125	1.9s	2.0s

The resulting relocated installation works as expected.

I suspect the Linux and Windows version of the tool could use the same optimization, but I won't be able to easily test on those platforms.

Backport: release