Add CPPFLAGS to compiler options (reported by blhc)

debian/patches/series

@@ -1,6 +1,7 @@
 # cherry-picked commits. Keep in upstream's chronological order
 
 # patches that should go upstream
+upstream.use-cppflags.patch
 upstream.fix-crash-on-huge-prefix-lists.patch
 upstream.fix-unaligned-memory-access.patch
 

debian/patches/upstream.use-cppflags.patch

@@ -0,0 +1,11 @@
+--- a/Makefile.in
++++ b/Makefile.in
+@@ -1,7 +1,7 @@
+ 
+ CC	= @CC@ -fPIC
+ CFLAGS	= @CFLAGS@
+-COMPILE  = $(CC) $(CFLAGS) $(INCLUDES)
++COMPILE  = $(CC) $(CFLAGS) $(CPPFLAGS) $(INCLUDES)
+ 
+ LD	= @CC@
+ LDFLAGS	= @LDFLAGS@