https://sources.debian.org/src/sks/1.1.6+git20200620.9e9d504-1/debian/patches/0008-accept-and-use-CFLAGS-and-CPPFLAGS-from-environment.patch/
----
From: Daniel Kahn Gillmor <dkg@fifthhorseman.net>
Date: Mon, 8 Aug 2016 13:20:38 -0400
Subject: accept and use CFLAGS and CPPFLAGS from environment

---
 Makefile     |  9 +++++----
 bdb/Makefile | 14 ++++++++------
 2 files changed, 13 insertions(+), 10 deletions(-)

--- a/Makefile
+++ b/Makefile
@@ -14,7 +14,7 @@
 #   Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307
 #   USA
 #
-CINCLUDES=-I`ocamlc -where`
+CINCLUDES=-I$(shell ocamlc -where)
 CFLAGS+=-O3 -Werror-implicit-function-declaration $(CINCLUDES) -I .
 CXXFLAGS+=-O3 $(CINCLUDES) -I .
 
@@ -43,6 +43,7 @@ else
 endif
 
 CAMLLDFLAGS=$(foreach x, $(LDFLAGS), -ccopt $(x))
+CAMLCFLAGS=$(foreach x, $(CFLAGS), -ccopt $(x)) $(foreach x, $(CPPFLAGS), -ccopt $(x))
 
 SKSVS=$(shell grep 'version_suffix = "+"' common.ml)
 ifeq ($(strip $(SKSVS)),)
@@ -52,7 +53,7 @@ WARNERR=-warn-error A
 endif
 
 CAMLINCLUDE= -package cryptokit,unix,str,bigarray,num -I bdb
-COMMONCAMLFLAGS=$(CAMLINCLUDE) $(OCAMLLIB) $(CAMLLDFLAGS) -ccopt -Lbdb -annot -bin-annot $(WARNERR)
+COMMONCAMLFLAGS=$(CAMLINCLUDE) $(OCAMLLIB) $(CAMLCFLAGS) $(CAMLLDFLAGS) -ccopt -Lbdb -annot -bin-annot $(WARNERR)
 OCAMLDEP=ocamldep
 CAMLLIBS=bdb.cma
 OCAMLFLAGS=$(COMMONCAMLFLAGS) -linkpkg -g $(CAMLLIBS)
--- a/bdb/Makefile
+++ b/bdb/Makefile
@@ -14,7 +14,7 @@
 # $Id: Makefile,v 1.6 2003/07/05 15:16:29 yminsky Exp $
 -include ../Makefile.local
 
-CINCLUDES=-I`ocamlc -where` $(BDBINCLUDE)
+CINCLUDES=-I$(shell ocamlc -where) $(BDBINCLUDE)
 CFLAGS+=-O3 -Werror-implicit-function-declaration $(CINCLUDES) $(BDBLIB) -I .
 CXXFLAGS+=-O3 $(CINCLUDES) $(BDBLIB) -I .
 
@@ -27,6 +27,8 @@ CAMLLIBS=unix.cma str.cma mylibs.cma
 OCAMLFLAGS=$(COMMONCAMLFLAGS) -g
 OCAMLOPTFLAGS=$(COMMONCAMLFLAGS) -inline 40
 
+CAMLCFLAGS=$(foreach x, $(CFLAGS), -ccopt $(x)) $(foreach x, $(CPPFLAGS), -ccopt $(x))
+
 ifndef LIBDB
 LIBDB=-ldb-4.6
 endif
@@ -37,7 +39,7 @@ ocextr: ocextr.ml
 	$(OCAMLC) -o ocextr ocextr.ml
 
 libbdb.a: $(COBJS)
-	$(MKLIB) -custom -o bdb $(COBJS)
+	$(MKLIB) $(CAMLCFLAGS) -custom -o bdb $(COBJS)
 
 bdb_stubs.o: bdb_stubs.h bdb_stubs.c
 
@@ -45,10 +47,10 @@ bdb.ml: ocextr bdb_stubs.c
 	./ocextr bdb_stubs.c > bdb.ml
 
 bdb.cma: bdb.cmo libbdb.a
-	$(MKLIB) -custom -o bdb bdb.cmo -lbdb $(LIBDB)
+	$(MKLIB) $(CAMLCFLAGS) -custom -o bdb bdb.cmo -lbdb $(LIBDB)
 
 bdb.cmxa: bdb.cmx libbdb.a
-	$(MKLIB) -custom -o bdb bdb.cmx -lbdb $(LIBDB)
+	$(MKLIB) $(CAMLCFLAGS) -custom -o bdb bdb.cmx -lbdb $(LIBDB)
 
 bdbcaml: bdb.cma
 	ocamlmktop -o bdbcaml -custom unix.cma bdb.cma $^