build: turn on transparent LFS support

Make sure we use 64-bit filesystem functions everywhere.  This applies not
only to being able to read large files (which generally doesn't apply to
us), but also being able to simply stat them (as they might be using large
inodes).

Makefile

@@ -49,6 +49,8 @@ CFLAGS ?= -O2 -g
 CFLAGS += -Wall
 CFLAGS += -fno-strict-aliasing # code needs a lot of work before strict aliasing is safe
 CPPFLAGS += -D_GNU_SOURCE
+# Turn on transparent support for LFS
+CPPFLAGS += -D_FILE_OFFSET_BITS=64 -D_LARGEFILE_SOURCE -D_LARGEFILE64_SOURCE
 RESLIB = # -L/usr/inet6/lib -linet6
 
 ifeq ($(HAVE_AFDECnet),1)