cuda dependency does not propagate into blt_add_executable

If you have a lib that depends on cuda:
```blt_add_library( NAME mylib DEPENDS_ON cuda )```
and a executable that depends on mylib:
```blt_add_executable( NAME myex DEPENDS_ON mylib)```
then myex doesn't inherit the cuda dependency from mylib...and bad things happen.

This is because the code here: https://github.com/LLNL/blt/blob/062ee3ff58e23713b9cd4d2daa2f9b5fca02d3bc/cmake/BLTMacros.cmake#L604
doesn't expand the dependencies. maybe the solution is to have a macro to expand the dependencies and use it prior to this check?

Start in cmake/BLTMacros.cmake at the dependency handling around line 604, using the blt_add_library and blt_add_executable examples in the issue to trace how dependencies are expanded. Reproduce the case where mylib depends on cuda and myex depends on mylib; done means myex inherits the cuda dependency.

Written by the indexing model from the issue text.