remove some visibility attributes/DLL storage

[compnerd]

Summary

When building libc++ with clang-cl, the duplicated annotation of these methods would cause an error.

cannot apply 'dllexport' to a 'dllexport' class

Since the class is already marked with the appropriate attribute, the function should inherit the visibility/DLL storage. Remove the secondary annotation.

[smeenai]

You beat me to this :)

[compnerd]

SVN r290785

include/optional

     bad_optional_access() : logic_error("bad optional access") {}
 
     // Get the key function ~bad_optional_access() into the dylib
-    _LIBCPP_FUNC_VIS
     virtual ~bad_optional_access() _NOEXCEPT;
 };
 

include/variant

 
 class _LIBCPP_EXCEPTION_ABI bad_variant_access : public exception {
 public:
-  _LIBCPP_FUNC_VIS virtual const char* what() const _NOEXCEPT;
+  virtual const char* what() const _NOEXCEPT;
 };
 
 } // namespace std