ExternalProject: Remove N^2 add_dependencies() calls

ExternalProject_Add_StepDependencies() contained a foreach() loop that
had another foreach() loop inside it iterating over the same set of values
(the dependencies). This resulted in add_dependencies() calls that added
the same dependencies to the step target N^2 times. A single call to
add_dependencies() with the list of dependencies provides the necessary
relationships without the N^2 behavior, and it removes the inner foreach()
loop.

Modules/ExternalProject.cmake

@@ -2746,12 +2746,10 @@ function(ExternalProject_Add_StepDependencies name step)
       OUTPUT ${stamp_file}
       DEPENDS ${dep}
     )
-    if(TARGET ${name}-${step})
-      foreach(dep ${dependencies})
-        add_dependencies(${name}-${step} ${dep})
-      endforeach()
-    endif()
   endforeach()
+  if(TARGET ${name}-${step})
+    add_dependencies(${name}-${step} ${dependencies})
+  endif()
 
 endfunction()