[PATCH] PR libstdc++/77691 fix resource_adaptor failures due to max_align_t bugs

[Jonathan Wakely <jwakely at redhat dot com>]

Remove the hardcoded whitelist of allocators expected to return memory
aligned to alignof(max_align_t), because that doesn't work when the
platform's malloc() and GCC's max_align_t do not agree what the largest
fundamental alignment is. It's also sub-optimal for user-defined
allocators that return memory suitable for any fundamental alignment.

Instead use a hardcoded list of alignments that are definitely supported
by the platform malloc, and use a copy of the allocator rebound to a POD
type with the requested alignment. Only allocate an oversized
buffer to use with std::align for alignments larger than any of the
hardcoded values.

For 32-bit Solaris x86 do not include alignof(max_align_t) in the
hardcoded values.

	PR libstdc++/77691
	* include/experimental/memory_resource: Add system header pragma.
	(__resource_adaptor_common::__guaranteed_alignment): Remove.
	(__resource_adaptor_common::_Types)
	(__resource_adaptor_common::__new_list)
	(__resource_adaptor_common::_New_list)
	(__resource_adaptor_common::_Alignments)
	(__resource_adaptor_common::_Fund_align_types): New utilities for
	creating a list of types with fundamental alignments.
	(__resource_adaptor_imp::do_allocate): Call new _M_allocate function.
	(__resource_adaptor_imp::do_deallocate): Call new _M_deallocate
	function.
	(__resource_adaptor_imp::_M_allocate): New function that first tries
	to use an allocator rebound to a type with a fundamental alignment.
	(__resource_adaptor_imp::_M_deallocate): Likewise for deallocation.
	* testsuite/experimental/memory_resource/new_delete_resource.cc:
	Adjust expected allocation sizes.
	* testsuite/experimental/memory_resource/resource_adaptor.cc: Remove
	xfail.

Tested x86_64-linux, committed to trunk.

Attachment: patch.txt
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