Use default visibility to work around clang -fvisibility-inlines-hidden bug
Clang (including trunk and many older versions) incorrectly marks static
local variables (__tag) hidden when -fvisibility-inlines-hidden is used.
This can lead to multiple instances of __tag when shares objects are used.
2018-07-20 Fangrui Song <maskray@google.com>
* include/bits/shared_ptr_base.h (_Sp_make_shared_tag::_S_ti): Use
_GLIBCXX_VISIBILITY(default).