qemu-kvm编译错误

今天编译了下qemu-kvm，死活编不过，错误信息如下：

CC    block/qcow2-snapshot.o
In file included from ./qemu-common.h:6:0,
                 from block/qcow2-snapshot.c:25:
block/qcow2-snapshot.c: In function ‘qcow2_write_snapshots’:
./compiler.h:36:23: error: typedef ‘qemu_build_bug_on__250’ locally defined but not used [-Werror=unused-local-typedefs]
     typedef char cat2(qemu_build_bug_on__,__LINE__)[(x)?-1:1];
                       ^
./compiler.h:33:18: note: in definition of macro ‘cat’
 #define cat(x,y) x ## y
                  ^
./compiler.h:36:18: note: in expansion of macro ‘cat2’
     typedef char cat2(qemu_build_bug_on__,__LINE__)[(x)?-1:1];
                  ^
block/qcow2-snapshot.c:249:5: note: in expansion of macro ‘QEMU_BUILD_BUG_ON’
     QEMU_BUILD_BUG_ON(offsetof(QCowHeader, snapshots_offset) !=
     ^
cc1: all warnings being treated as errors

说是把警告都当错误处理，但这不是自己的代码，要消除警告啥弄啊。后来在Makefile里添加了下面一行：

QEMU_CFLAGS+=-w

再次编译成功了。