In a Debian Linux environment, it's not a good idea, apparently, to

manually declare the include directory /usr/include at the same time
as the macro PROTOTYPES is defined with the value 1.  Besides,
/usr/include is the standard include directory anyway, so there's no
need to specify it explicitely.

demos/engines/rsaref/Makefile

@@ -27,7 +27,7 @@ all:
 FORCE.install:
 install:	FORCE.install
 		cd install; \
-			make -f unix/makefile INCL='-I. -I/usr/include' CFLAGS='$(INCL) -O -c' RSAREFLIB=librsaref.a librsaref.a
+			make -f unix/makefile CFLAGS='-I. -DPROTOTYPES=1 -O -c' RSAREFLIB=librsaref.a librsaref.a
 
 gnu:		install $(SHLIB).gnu
 tru64:		install $(SHLIB).tru64