patch 8.0.1378: autoload script sources itself when defining function

Problem:    Autoload script sources itself when defining function.
Solution:   Pass TFN_NO_AUTOLOAD to trans_function_name(). (Yasuhiro
            Matsumoto, closes #2423)
diff --git a/src/testdir/sautest/autoload/sourced.vim b/src/testdir/sautest/autoload/sourced.vim
new file mode 100644
index 0000000..f69f00c
--- /dev/null
+++ b/src/testdir/sautest/autoload/sourced.vim
@@ -0,0 +1,3 @@
+let g:loaded_sourced_vim += 1
+func! sourced#something()
+endfunc