Fix nasa#2481, correct loop variable

This CMake loop is supposed to run for every app.  Unfortunately at
this point the SYSVAR is not yet defined, so the result is it does
nothing and none of the overrides get configured.

With this loop, it should set up the override directive correctly.

cmake/arch_build.cmake

@@ -666,7 +666,7 @@ function(setup_platform_msgids)
       list(APPEND OUTPUT_VAR_LIST ${CFGSRC}_cfe_${DEP_NAME}_msgids)
     endforeach(DEP_NAME ${MISSION_CORE_MODULES})
 
-    foreach(DEP_NAME ${TGTSYS_${SYSVAR}_APPS} ${TGTSYS_${SYSVAR}_STATICAPPS})
+    foreach(DEP_NAME ${MISSION_APPS})
       string(TOUPPER "${DEP_NAME}_CFGFILE_SRC" CFGSRC)
       list(APPEND OUTPUT_VAR_LIST ${CFGSRC}_${DEP_NAME}_msgids)
     endforeach(DEP_NAME ${MISSION_APPS})