Don't try to use nonexistent global attribute id constants on Darwin.

[bzbarsky-apple]

We have some global attributes that are marked provisional. New clusters being added would try to generate a constant for the global attribute inside the cluster, until we had a chance to set it provisional, but set its value to the nonexistent global constant, which would fail to compile.

This just skips generating the relevant cluster constants and the methods that use them.

[github-actions]

PR #26398: Size comparison from fc0a2fb to c243e29

Increases (1 build for cc32xx)

platform	target	config	section	fc0a2fb	c243e29	change	% change
cc32xx	lock	CC3235SF_LAUNCHXL	.debug_info	19609712	19609713	1	0.0

Full report (1 build for cc32xx)

platform	target	config	section	fc0a2fb	c243e29	change	% change
cc32xx	lock	CC3235SF_LAUNCHXL		0	0	0	0.0
			(read only)	605058	605058	0	0.0
			(read/write)	204164	204164	0	0.0
			.ARM.attributes	44	44	0	0.0
			.ARM.exidx	8	8	0	0.0
			.bss	197576	197576	0	0.0
			.comment	206	206	0	0.0
			.data	1468	1468	0	0.0
			.debug_abbrev	957621	957621	0	0.0
			.debug_aranges	101136	101136	0	0.0
			.debug_frame	341512	341512	0	0.0
			.debug_info	19609712	19609713	1	0.0
			.debug_line	2666606	2666606	0	0.0
			.debug_line_str	513	513	0	0.0
			.debug_loc	33340	33340	0	0.0
			.debug_loclists	1489165	1489165	0	0.0
			.debug_ranges	4984	4984	0	0.0
			.debug_rnglists	94315	94315	0	0.0
			.debug_str	3108961	3108961	0	0.0
			.ramVecs	780	780	0	0.0
			.resetVecs	64	64	0	0.0
			.rodata	104354	104354	0	0.0
			.shstrtab	265	265	0	0.0
			.stack	2048	2048	0	0.0
			.strtab	483384	483384	0	0.0
			.symtab	287328	287328	0	0.0
			.text	498580	498580	0	0.0

[bzbarsky-apple]

Fast-tracking platform-specific change with platform owner review.