Task #8021: Added check for existing target to lofar_create_target_symlink()....

Task #8021: Added check for existing target to lofar_create_target_symlink(). Take two, which is hopefully correct now.

CMake/LofarMacros.cmake

@@ -213,6 +213,10 @@ if(NOT DEFINED LOFAR_MACROS_INCLUDED)
   # use of the generator expression $<TARGET_FILE>.
   # --------------------------------------------------------------------------
   macro(lofar_create_target_symlink _target _symlink)
+    if(NOT TARGET ${_target})
+      message(SEND_ERROR
+        "Cannot create symbolic link to non-existing target ${_target}")
+    endif(NOT TARGET ${_target})
     if(POLICY CMP0026)
       set(_location $<TARGET_FILE:${_target}>)
     else(POLICY CMP0026)