patch 9.1.0431: eval.c is too long

Problem:  eval.c is too long
Solution: Move garbage collection code to new gc.c file
          (Yegappan Lakshmanan)

closes: #14824

Signed-off-by: Yegappan Lakshmanan <yegappan@yahoo.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>
diff --git a/src/proto.h b/src/proto.h
index 50802ce..94e34b0 100644
--- a/src/proto.h
+++ b/src/proto.h
@@ -94,6 +94,7 @@
 # include "float.pro"
 # include "fold.pro"
 # include "getchar.pro"
+# include "gc.pro"
 # include "gui_xim.pro"
 # include "hardcopy.pro"
 # include "hashtab.pro"