libstdc++: Guard use of sized deallocation [PR114940]

libstdc++: Guard use of sized deallocation [PR114940]

Clang does not enable -fsized-deallocation by default, which means it
can't compile our <stacktrace> and <generator> headers.

Make the __cpp_lib_generator macro depend on the compiler-defined
__cpp_sized_deallocation macro, and change <stacktrace> to use unsized
deallocation when __cpp_sized_deallocation isn't defined.

libstdc++-v3/ChangeLog:

	PR libstdc++/114940
	* include/bits/version.def (generator): Depend on
	__cpp_sized_deallocation.
	* include/bits/version.h: Regenerate.
	* include/std/stacktrace (_GLIBCXX_SIZED_DELETE): New macro.
	(basic_stacktrace::_Impl::_M_deallocate): Use it.