Objective-C, Darwin: Do not overalign CFStrings and Objective-C metadata.

Objective-C, Darwin: Do not overalign CFStrings and Objective-C metadata.

We have reports of regressions in both Objective-C and Objective-C++ on
Darwin23 (macOS 14).  In some cases, these are linker warnings about the
alignment of CFString constants; in other cases the built executables
crash during runtime initialization.  The underlying issue is the same in
both cases; since the objects (CFStrings, Objective-C meta-data) are TU-
local, we are choosing to increase their alignment for efficiency - to
values greater than ABI alignment.

However, although these objects are TU-local, they are also visible to the
linker (since they are placed in specific named sections).  In many cases
the metadata can be regarded as tables of data, and thus it is expected
that these sections can be concatenated from multiple TUs and the data
treated as tabular.  In order for this to work the data cannot be allowed
to exceed ABI alignment - which leads to the crashes.

For GCC-15+ it would be nice to find a more elegant solution to this issue
(perhaps by adjusting the concept of binds-locally to exclude specific
named sections) - but I do not want to do that in stage 4.

The solution here is to force the alignment to be preserved as created by
setting DECL_USER_ALIGN on the relevant objects.

gcc/ChangeLog:

	* config/darwin.cc (darwin_build_constant_cfstring): Prevent over-
	alignment of CFString constants by setting DECL_USER_ALIGN.

gcc/objc/ChangeLog:

	* objc-next-runtime-abi-02.cc (build_v2_address_table): Prevent
	over-alignment of Objective-C metadata by setting DECL_USER_ALIGN
	on relevant variables.
	(build_v2_protocol_list_address_table): Likewise.
	(generate_v2_protocol_list): Likewise.
	(generate_v2_meth_descriptor_table): Likewise.
	(generate_v2_meth_type_list): Likewise.
	(generate_v2_property_table): Likewise.
	(generate_v2_dispatch_table): Likewise.
	(generate_v2_ivars_list): Likewise.
	(generate_v2_class_structs): Likewise.
	(build_ehtype): Likewise.
	* objc-runtime-shared-support.cc (generate_strings): Likewise.

Signed-off-by: Iain Sandoe <iain@sandoe.co.uk>