Unify Python3_Development_FOUND checks (#1541)

The value of this variable may change if other code paths
call find_package(Python3), so move the warning to be
co-located with the add_subdirectory call.

Signed-off-by: Steve Peters <[email protected]>

Author: scpeters

CMakeLists.txt

@@ -95,9 +95,6 @@ if (BUILD_SDF)
       COMPONENTS Interpreter
       OPTIONAL_COMPONENTS Development
     )
-    if (NOT Python3_Development_FOUND)
-      GZ_BUILD_WARNING("Python development libraries are missing: Python interfaces are disabled.")
-    endif()
   endif()
 
   #################################################
@@ -151,8 +148,12 @@ if (BUILD_SDF)
   add_subdirectory(sdf)
   add_subdirectory(conf)
   add_subdirectory(doc)
-  if (Python3_Development_FOUND AND NOT SKIP_PYBIND11)
-    add_subdirectory(python)
+  if (NOT SKIP_PYBIND11)
+    if (Python3_Development_FOUND)
+      add_subdirectory(python)
+    else()
+      message(WARNING "Python development libraries are missing: Python interfaces are disabled.")
+    endif()
   endif()
 endif(BUILD_SDF)