[libc++] Make _LIBCPP_TYPE_VIS export members

Summary:
Most classes annotated with _LIBCPP_TYPE_VIS need to have at least some
of their members exported, otherwise we have a lot of link errors when
linking against a libc++ built with hidden visibility. This also makes
_LIBCPP_TYPE_VIS be consistent across platforms, since on Windows it
already exports members.

With this change made, any template methods of a class marked
_LIBCPP_TYPE_VIS will also get default visibility when instantiatied,
which is not desirable for clients of libc++ headers who wish to control
their visibility; this is the same issue as PR30642. Annotate all
problematic methods with an explicit visibility specifier to avoid this.

The problematic methods were found by running bad-visibility-finder [1]
against the libc++ headers after making the _LIBCPP_TYPE_VIS change. The
small methods were marked for inlining; the larger ones hidden.

[1] https://github.com/smeenai/bad-visibility-finder

Reviewers: mclow.lists, EricWF

Subscribers: cfe-commits

Differential Revision: https://reviews.llvm.org/D25208

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@296732 91177308-0d34-0410-b5e6-96231b3b80d8

include/condition_variable

@@ -133,12 +133,14 @@ public:
     void notify_all() _NOEXCEPT;
 
     template <class _Lock>
+        _LIBCPP_METHOD_TEMPLATE_IMPLICIT_INSTANTIATION_VIS
         void wait(_Lock& __lock);
     template <class _Lock, class _Predicate>
         _LIBCPP_INLINE_VISIBILITY
         void wait(_Lock& __lock, _Predicate __pred);
 
     template <class _Lock, class _Clock, class _Duration>
+        _LIBCPP_METHOD_TEMPLATE_IMPLICIT_INSTANTIATION_VIS
         cv_status
         wait_until(_Lock& __lock,
                    const chrono::time_point<_Clock, _Duration>& __t);