remove some inherited attributes on exceptions

These exception types are marked with `_LIBCPP_EXCEPTION_ABI` which
expands to `__attribute__((__visibility__("default")))` or
`__declspec(dllexport)`.  When building for Windows, we would hit an
error:

    cannot apply 'dllexport' to a 'dllexport' class

Remove the duplicate annotations as they will be inherited from the
class.

llvm-svn: 290785

libcxx/include/optional

@@ -167,7 +167,6 @@ public:
     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;
 };
 

libcxx/include/variant

@@ -216,7 +216,7 @@ namespace std { // explicitly not using versioning namespace
 
 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