honor user CFLAGS. honor the CFLAGS when generating uoff_t.h, because
it may include flags like -m32 or -m64 and the result would be incorrect
if we ignore them.

diff -urN lxsplit-0.2.2/Makefile lxsplit-0.2.2.1/Makefile
--- lxsplit-0.2.2/Makefile	2008-03-22 12:32:07.000000000 +0200
+++ lxsplit-0.2.2.1/Makefile	2008-05-31 10:55:25.000000000 +0300
@@ -13,7 +13,8 @@
 CC	:=	gcc
 endif
 INCPATH :=	.
-CFLAGS	:=	-Wall -W -O2 -DNO_DEBUG
+CFLAGS	?=	-O2
+CFLAGS	:=	$(CFLAGS) -Wall -W -DNO_DEBUG
 LDLIBS	:=	
 LDFLAGS	:=	
 
@@ -54,7 +55,7 @@
 	$(CC) $(LDFLAGS) -o $(BINARY) $(OBJECTS) $(LDLIBS)
 
 uoff_t.h: mkuoff_t.c
-	$(CC) $(FILESIZE_DEFS) -o mkuoff_t mkuoff_t.c
+	$(CC) $(CFLAGS) $(FILESIZE_DEFS) -o mkuoff_t mkuoff_t.c
 	@echo "Generating uoff_t.h"
 	@./mkuoff_t