CMakeLists.txt should not define a fixed list of dependent applications

[DavidEdell]

Describe the bug
If a different set of dependencies is needed, then the build process will fail. This makes it impossible to utilize to_lab in a system without modifying the upstream repository. The TO table can be easily overridden in the build process (ie: copying to sample_defs/tables/to_lab_sub.c), but the include list is currently fixed.

Proposed change
The foreach line in CMakeLists.txt can be changed to use a CMake macro
foreach(EXT_APP ${${TGTSYS_${SYSVAR}}_APPLIST})

NOTE: This issue also applies to sch_lab.