--- libhugetlbfs-2.20/tests/Makefile	2018-04-10 02:00:33.613966578 +0200
+++ libhugetlbfs-2.20/tests/Makefile	2015-12-04 03:04:07.000000000 +0100
@@ -33,8 +33,8 @@
 HELPER_LIBS = libheapshrink.so
 BADTOOLCHAIN = bad-toolchain.sh
 
-CFLAGS = -O2 -Wall -g
-CPPFLAGS = -I..
+CFLAGS ?= -O2 -Wall -g
+CPPFLAGS += -I..
 STATIC_LIBHUGE = -Wl,--whole-archive -lhugetlbfs -Wl,--no-whole-archive
 STATIC_LDLIBS = -Wl,--no-as-needed -lpthread
 LDLIBS = $(STATIC_LDLIBS) -ldl -lhugetlbfs_privutils