CMake adjust Linux build

Instead of linking the same target name and re-building, we can install
the file to a new name.  This speeds the build process and keeps linking
routines from stepping on each other.  Available now that we are at
CMake 3.0.2

Fixes: lp:1789468
* https://bugs.launchpad.net/kicad/+bug/1789468

pcbnew/CMakeLists.txt

@@ -773,11 +773,7 @@ if( KICAD_SCRIPTING_MODULES )
         add_dependencies( ScriptingModulesPcbnewSoCopy ScriptingWxpythonCopy )
         set( PYMOD_EXT "so" )
     else()  # only linux remains among supported platforms
-        add_library( pcbnew_python MODULE $<TARGET_OBJECTS:pcbnew_kiface_objects> )
-        target_link_libraries( pcbnew_python ${PCBNEW_KIFACE_LIBRARIES} )
-        set_target_properties( pcbnew_python PROPERTIES OUTPUT_NAME pcbnew PREFIX "_" SUFFIX ".so" )
-        install( TARGETS pcbnew_python DESTINATION ${PYTHON_DEST} COMPONENT binary )
-
+        install( FILES ${CMAKE_CURRENT_BINARY_DIR}/_pcbnew.kiface DESTINATION ${PYTHON_DEST} COMPONENT binary RENAME "_pcbnew.so" )
         set( PYMOD_EXT "so" )
     endif()
 
@@ -792,8 +788,6 @@ if( KICAD_SCRIPTING_MODULES )
             DEPENDS ${CMAKE_CURRENT_BINARY_DIR}/_pcbnew.${PYMOD_EXT}
             )
     else()
-
-
         # For phase 1, copy _pcbnew.kiface to the python module.
         add_custom_command( OUTPUT ${CMAKE_CURRENT_BINARY_DIR}/_pcbnew.${PYMOD_EXT}
             DEPENDS pcbnew_kiface