U64toa 单元测试用例不通过

[lkkey80]

GCC(devtoolset 8.3.1) -O2优化编译(同时去掉-fsanitize=address)的时候，U64toa有部分测试用例结果不正确

[----------] 1 test from U64toa
[ RUN ] U64toa.Basic
sonic-cpp.git/tests/itoa_test.cpp:34: Failure
Expected equality of these values:
expect.data()
Which is: "12345"
buf
Which is: "10345"
sonic-cpp.git/tests/itoa_test.cpp:34: Failure
Expected equality of these values:
expect.data()
Which is: "1234567890123"
buf
Which is: "1034567890123"
[ FAILED ] U64toa.Basic (0 ms)
[----------] 1 test from U64toa (0 ms total)