File ocamlnet-4.1.6.old/src/netsys/configtests/mkfifoat_test is a fifo while file ocamlnet-4.1.6/src/netsys/configtests/mkfifoat_test is a fifo
diff -ur ocamlnet-4.1.6.old/src/netsys/netsys_c.h ocamlnet-4.1.6/src/netsys/netsys_c.h
--- ocamlnet-4.1.6.old/src/netsys/netsys_c.h	2018-05-08 08:42:00.000000000 +0100
+++ ocamlnet-4.1.6/src/netsys/netsys_c.h	2020-01-19 16:34:54.461449380 +0000
@@ -122,6 +122,7 @@
 
 #define Is_in_heap(a) (Classify_addr(a) & In_heap)
 
+#if 0
 /* Stuff from minor_gc.h */
 
 CAMLextern char *caml_young_start;
@@ -150,6 +151,7 @@
 #define Phase_mark 0
 
 extern void caml_darken (value, value *);
+#endif
 
 #endif
 
diff -ur ocamlnet-4.1.6.old/src/netsys/netsys_c_outofheap.c ocamlnet-4.1.6/src/netsys/netsys_c_outofheap.c
--- ocamlnet-4.1.6.old/src/netsys/netsys_c_outofheap.c	2018-05-08 08:42:00.000000000 +0100
+++ ocamlnet-4.1.6/src/netsys/netsys_c_outofheap.c	2020-01-19 16:35:41.530802566 +0000
@@ -9,6 +9,8 @@
 
 #include "netsys_c.h"
 
+#if 0
+
 #ifdef HAVE_NEW_MODIFY
 /* implies FANCY_PAGE_TABLES */
 
@@ -42,3 +44,4 @@
 }
 
 #endif
+#endif