[CMake] How to add dependencies to ExternalProject_Add()

[Rolf Eike Beer]

> I came up with this simple diff which makes everything work smoothly for
> me:

This also works for me and should properly detect if the dependency is
itself an external target or not:

diff --git a/Modules/ExternalProject.cmake b/Modules/ExternalProject.cmake
index 3de6b7e..90b23ce 100644
--- a/Modules/ExternalProject.cmake
+++ b/Modules/ExternalProject.cmake
@@ -1261,8 +1261,14 @@ function(_ep_add_configure_command name)
   set(file_deps)
   get_property(deps TARGET ${name} PROPERTY _EP_DEPENDS)
   foreach(dep IN LISTS deps)
+    # Find out if this dependency is itself an external target or not.
+    # If it doesn't have _EP_STAMP_DIR we assume it's a normal target.
     get_property(dep_stamp_dir TARGET ${dep} PROPERTY _EP_STAMP_DIR)
-    list(APPEND file_deps ${dep_stamp_dir}${cfgdir}/${dep}-done)
+    if(dep_stamp_dir)
+      list(APPEND file_deps ${dep_stamp_dir}${cfgdir}/${dep}-done)
+    else(dep_stamp_dir)
+      list(APPEND file_deps ${dep})
+    endif(dep_stamp_dir)
   endforeach()

   get_property(cmd_set TARGET ${name} PROPERTY _EP_CONFIGURE_COMMAND SET)

Eike