patch 8.2.3860: Vim9: codecov struggles with the file size

Problem:    Vim9: codecov struggles with the file size.
Solution:   Split vim9compile.c into four files.
diff --git a/src/vim9script.c b/src/vim9script.c
index 90c39f9..72c7088 100644
--- a/src/vim9script.c
+++ b/src/vim9script.c
@@ -13,7 +13,8 @@
 
 #include "vim.h"
 
-#if defined(FEAT_EVAL)
+// When not generating protos this is included in proto.h
+#ifdef PROTO
 # include "vim9.h"
 #endif