Fix the removal of Sun RPC interfaces from glibc

SunPRC had been moved from glibc to libtirpc project,
rpc/rpc.h is a tirpc/rpc/rpc.h now.

--- Makefile.am
+++ Makefile.am
@@ -29,7 +29,7 @@
 tricklectl_SOURCES = tricklectl.c trickledu.c atomicio.c xdr.c
 tricklectl_LDADD = @ERRO@  -lbsd
 
-AM_CFLAGS = -Wall -Icompat @EVENTINC@
+AM_CFLAGS = -Wall -Icompat -I/usr/include/tirpc -ltirpc @EVENTINC@
 
 overloaddir = $(libdir)
 #overload_DATA = libtrickle.so