CMake 2.8.12 and lower allowed the SOURCE signature in add_custom_command

In CMake 3.0 the policy CMP0050 was introduced where it could be set to OLD to keep this behaviour while for NEW an error was raised.
Since CMake 3.5.2 a warning comes up when using the OLD behaviour and that it will be removed in a future version.

In FreeCAD we switched to the new behaviour now and removed the SOURCE signature from add_custom_command which affects the macros
fc_copy_sources, fc_target_copy_resource and fc_target_copy_resource_flat and their usage.
It's not possible any more to add files to a target by using the macros. Now a file must be added to the target before using the macros.

This commit fixes it for Arch, Draft, OpenSCAD, Material, Plot and Ship

src/Mod/Material/CMakeLists.txt

@@ -40,7 +40,7 @@ ADD_CUSTOM_TARGET(Material ALL
 )
 
 fc_target_copy_resource(Material 
-    ${CMAKE_SOURCE_DIR}/src/Mod/Material
+    ${CMAKE_CURRENT_SOURCE_DIR}
     ${CMAKE_BINARY_DIR}/Mod/Material
     ${Material_SRCS})
 
@@ -61,11 +61,11 @@ ADD_CUSTOM_TARGET(FluidMaterialLib ALL
 # When a target copies files to different output directories then apparently it always builds the project
 # which is very annoying. So, the trick is to split this into two targets to avoid this behaviour.
 fc_target_copy_resource(MaterialLib 
-    ${CMAKE_SOURCE_DIR}/src/Mod/Material
+    ${CMAKE_CURRENT_SOURCE_DIR}
     ${CMAKE_BINARY_DIR}/${CMAKE_INSTALL_DATADIR}/Mod/Material
     ${MaterialLib_Files})
 fc_target_copy_resource(FluidMaterialLib 
-    ${CMAKE_SOURCE_DIR}/src/Mod/Material
+    ${CMAKE_CURRENT_SOURCE_DIR}
     ${CMAKE_BINARY_DIR}/${CMAKE_INSTALL_DATADIR}/Mod/Material
     ${FluidMaterial_Files})