libstdc++: Deprecate std::unexpected and handler functions

libstdc++: Deprecate std::unexpected and handler functions

These functions have been deprecated since C++11, and were removed in
C++17. The proposal P0323 wants to reuse the name std::unexpected for a
class template, so we will need to stop defining the current function
for C++23 anyway.

This marks them as deprecated for C++11 and up, to warn users they won't
continue to be available. It disables them for C++17 and up, unless the
_GLIBCXX_USE_DEPRECATED macro is defined.

The <unwind-cxx.h> header uses std::unexpected_handler in the public
API, but since that type is the same as std::terminate_handler we can
just use that instead, to avoid warnings about it being deprecated.

libstdc++-v3/ChangeLog:

	* doc/xml/manual/evolution.xml: Document deprecations.
	* doc/html/*: Regenerate.
	* libsupc++/exception (unexpected_handler, unexpected)
	(get_unexpected, set_unexpected): Add deprecated attribute.
	Do not define without _GLIBCXX_USE_DEPRECATED for C++17 and up.
	* libsupc++/eh_personality.cc (PERSONALITY_FUNCTION): Disable
	deprecated warnings.
	* libsupc++/eh_ptr.cc (std::rethrow_exception): Likewise.
	* libsupc++/eh_terminate.cc: Likewise.
	* libsupc++/eh_throw.cc (__cxa_init_primary_exception):
	Likewise.
	* libsupc++/unwind-cxx.h (struct __cxa_exception): Use
	terminate_handler instead of unexpected_handler.
	(struct __cxa_dependent_exception): Likewise.
	(__unexpected): Likewise.
	* testsuite/18_support/headers/exception/synopsis.cc: Add
	dg-warning for deprecated warning.
	* testsuite/18_support/exception_ptr/60612-unexpected.cc:
	Disable deprecated warnings.
	* testsuite/18_support/set_unexpected.cc: Likewise.
	* testsuite/18_support/unexpected_handler.cc: Likewise.

gcc/testsuite/ChangeLog:

	* g++.dg/cpp0x/lambda/lambda-eh2.C: Add dg-warning for new
	deprecation warnings.
	* g++.dg/cpp0x/noexcept06.C: Likewise.
	* g++.dg/cpp0x/noexcept07.C: Likewise.
	* g++.dg/eh/forced3.C: Likewise.
	* g++.dg/eh/unexpected1.C: Likewise.
	* g++.old-deja/g++.eh/spec1.C: Likewise.
	* g++.old-deja/g++.eh/spec2.C: Likewise.
	* g++.old-deja/g++.eh/spec3.C: Likewise.
	* g++.old-deja/g++.eh/spec4.C: Likewise.
	* g++.old-deja/g++.mike/eh33.C: Likewise.
	* g++.old-deja/g++.mike/eh34.C: Likewise.
	* g++.old-deja/g++.mike/eh50.C: Likewise.
	* g++.old-deja/g++.mike/eh51.C: Likewise.