diff -uNr lmdb-LMDB_0.9.24/libraries/liblmdb/Makefile lmdb-LMDB_0.9.24.mod/libraries/liblmdb/Makefile
--- lmdb-LMDB_0.9.24/libraries/liblmdb/Makefile	2019-07-19 19:41:12.000000000 +0300
+++ lmdb-LMDB_0.9.24.mod/libraries/liblmdb/Makefile	2020-01-24 20:00:21.378688952 +0200
@@ -18,8 +18,8 @@
 # There may be other macros in mdb.c of interest. You should
 # read mdb.c before changing any of them.
 #
-CC	= gcc
-AR	= ar
+CC	?= gcc
+AR	?= ar
 W	= -W -Wall -Wno-unused-parameter -Wbad-function-cast -Wuninitialized
 THREADS = -pthread
 OPT = -O2 -g
@@ -27,7 +27,7 @@
 LDLIBS	=
 SOLIBS	=
 SOEXT	= .so
-prefix	= /usr/local
+prefix	?= /usr/local
 exec_prefix = $(prefix)
 bindir = $(exec_prefix)/bin
 libdir = $(exec_prefix)/lib