patch 8.2.3301: memory allocation functions don't have their own place

Problem:    Memory allocation functions don't have their own place.
Solution:   Move memory allocation functions to alloc.c.  (Yegappan
            Lakshmanan, closes #8717)
diff --git a/src/proto.h b/src/proto.h
index f639ad5..6c26aee 100644
--- a/src/proto.h
+++ b/src/proto.h
@@ -58,6 +58,7 @@
 #  include "crypt.pro"
 #  include "crypt_zip.pro"
 # endif
+# include "alloc.pro"
 # include "arglist.pro"
 # include "autocmd.pro"
 # include "buffer.pro"