Fix -Wdeprecated-copy-dtor and -Wdeprecated-dynamic-exception-spec warnings.

Summary:
The former are like:

libcxx/include/typeinfo:322:11: warning: definition of implicit copy constructor for 'bad_cast' is deprecated because it has a user-declared destructor [-Wdeprecated-copy-dtor]
  virtual ~bad_cast() _NOEXCEPT;
          ^
libcxx/include/typeinfo:344:11: note: in implicit copy constructor for 'std::bad_cast' first required here
    throw bad_cast();
          ^

Fix these by adding an explicitly defaulted copy constructor.

The latter are like:

libcxx/include/codecvt:105:37: warning: dynamic exception specifications are deprecated [-Wdeprecated-dynamic-exception-spec]
    virtual int do_encoding() const throw();
                                    ^~~~~~~

Fix these by using the _NOEXCEPT macro instead.

Reviewers: EricWF, mclow.lists, ldionne, #libc

Reviewed By: EricWF, #libc

Subscribers: dexonsmith, libcxx-commits

Tags: #libc

Differential Revision: https://reviews.llvm.org/D76150

Cr-Mirrored-From: https://chromium.googlesource.com/external/github.com/llvm/llvm-project
Cr-Mirrored-Commit: 585a3cc31bb49f2a526dcb74dc9a980379193f93
diff --git a/include/filesystem b/include/filesystem
index 0f7a4d5..1363b63 100644
--- a/include/filesystem
+++ b/include/filesystem
@@ -1346,6 +1346,7 @@
   _LIBCPP_INLINE_VISIBILITY
   const path& path2() const noexcept { return __storage_->__p2_; }
 
+  filesystem_error(const filesystem_error&) = default;
   ~filesystem_error() override; // key function
 
   _LIBCPP_INLINE_VISIBILITY