cmake: s/Python_EXECUTABLE/Python3_EXECUTABLE/

as FindPython3.cmake only sets Python3_EXECUTABLE for us, we should
stick with Python3_EXECUTABLE instead of Python_EXECUTABLE.

Signed-off-by: Kefu Chai <kchai@redhat.com>

src/common/options/CMakeLists.txt

@@ -33,7 +33,7 @@ function(add_options name)
   set(h_file "${PROJECT_BINARY_DIR}/include/${name}_legacy_options.h")
   add_custom_command(PRE_BUILD
     OUTPUT ${cc_file} ${h_file}
-    COMMAND ${Python_EXECUTABLE} ${CMAKE_CURRENT_SOURCE_DIR}/y2c.py
+    COMMAND ${Python3_EXECUTABLE} ${CMAKE_CURRENT_SOURCE_DIR}/y2c.py
       --input ${yaml_file}
       --output ${cc_file}
       --legacy ${h_file}