[libc++] Fix visibility of __vector_base_common on GCC

Since we build the library with -fvisibility=hidden, the shared object
wouldn't contain __vector_base_common<true>::__throw_length_error()
and __vector_base_common<true>::__throw_out_of_range(), leading to
link errors. This only happened on GCC for some reason.

https://llvm.org/PR43140

llvm-svn: 370240

libcxx/include/vector

@@ -297,7 +297,7 @@ _LIBCPP_PUSH_MACROS
 _LIBCPP_BEGIN_NAMESPACE_STD
 
 template <bool>
-class __vector_base_common
+class _LIBCPP_TEMPLATE_VIS __vector_base_common
 {
 protected:
     _LIBCPP_INLINE_VISIBILITY __vector_base_common() {}