build: avoid using 'INCLUDES' in Makefile.am

Avoids warnings during build; e.g.:
    warning: 'INCLUDES' is the old name for 'AM_CPPFLAGS' (or '*_CPPFLAGS')

libqcdm/tests/Makefile.am

@@ -3,10 +3,6 @@ include $(top_srcdir)/gtester.make
 noinst_PROGRAMS = test-qcdm modepref ipv6pref
 TEST_PROGS += test-qcdm
 
-INCLUDES = \
-	-I$(top_srcdir)/libqcdm/src \
-	-I$(top_srcdir)/src
-
 test_qcdm_SOURCES = \
 	test-qcdm-crc.c \
 	test-qcdm-crc.h \
@@ -19,15 +15,24 @@ test_qcdm_SOURCES = \
 	test-qcdm-result.c \
 	test-qcdm-result.h \
 	test-qcdm.c
-test_qcdm_CPPFLAGS = $(MM_CFLAGS)
+test_qcdm_CPPFLAGS = \
+	$(MM_CFLAGS) \
+	-I$(top_srcdir)/libqcdm/src \
+	-I$(top_srcdir)/src
 test_qcdm_LDADD = $(MM_LIBS)
 
 modepref_SOURCES = modepref.c
-modepref_CPPFLAGS = $(MM_CFLAGS)
+modepref_CPPFLAGS = \
+	$(MM_CFLAGS) \
+	-I$(top_srcdir)/libqcdm/src \
+	-I$(top_srcdir)/src
 modepref_LDADD = $(MM_LIBS)
 
 ipv6pref_SOURCES = ipv6pref.c
-ipv6pref_CPPFLAGS = $(MM_CFLAGS)
+ipv6pref_CPPFLAGS = \
+	$(MM_CFLAGS) \
+	-I$(top_srcdir)/libqcdm/src \
+	-I$(top_srcdir)/src
 ipv6pref_LDADD = $(MM_LIBS)
 
 if QCDM_STANDALONE