Support gcc7

[herumi]

gcc 7 put the following message, then I add -faligned-new option, but I don't know that it is best way.

src/counter/handler.cpp: In member function 'std::unique_ptr<cybozu::tcp_socket> yrmcds::counter::handler::make_counter_socket(int)':
src/counter/handler.cpp:72:47: warning: 'new' of type 'yrmcds::counter::counter_socket' with extended alignment 64 [-Waligned-new=]
         new counter_socket(s, m_finder, m_hash) );

[nojima]

I'll take a look later.

[nojima]

I've got what the warning says.

When allocating an object whose alignment is larger than alignof(max_align_t) by using new-expression, the result is implementation-defined.

GCC 6 seems to ignore alignas(64), and allocates the object aligned as 16 byes.
I confirmed that GCC 7 respects alignas(64) when -faligned-new is specified.

[nojima]

Rather than -faligned-new, I would like to remove alignas(CACHE_LINE_SIZE) from yrmcds::counter::counter_socket.
We can safely remove it because it is virtually not working until now.

It is not too late to use alignas after contentions among threads get to be real problem.

[ymmt2005]

@nojima Agreed. Thank you for your investigation.

[ymmt2005]

@herumi
Could you please drop commit 50a5092 from this PR?
I will take over the alignment problems in another commit.

[ymmt2005]

merged. Thank you!

[ymmt2005]

The alignment problem will be addressed in #71. @nojima