Building fuzzing logic was not well documented

[andy31415]

Updated build_examples.py to support fuzzing:

• set a propper target when using fuzzing for tests (only build a subset otherwise all other tests will have duplicate main)
• support ossfuzz as an option for build_examples
• Add a bit of documentation for this

Note that ossfuzz still fails for me with "no main defined" even when using instructions from #26010 - following up on that. For now this just makes things better and working at least for libfuzzer.

[github-actions]

PR #26298: Size comparison from 77d72a8 to f3c99c5

Full report (1 build for cc32xx)

platform	target	config	section	77d72a8	f3c99c5	change	% change
cc32xx	lock	CC3235SF_LAUNCHXL		0	0	0	0.0
			(read only)	602714	602714	0	0.0
			(read/write)	204156	204156	0	0.0
			.ARM.attributes	44	44	0	0.0
			.ARM.exidx	8	8	0	0.0
			.bss	197568	197568	0	0.0
			.comment	206	206	0	0.0
			.data	1468	1468	0	0.0
			.debug_abbrev	956984	956984	0	0.0
			.debug_aranges	103664	103664	0	0.0
			.debug_frame	350552	350552	0	0.0
			.debug_info	19521972	19521972	0	0.0
			.debug_line	2682751	2682751	0	0.0
			.debug_line_str	513	513	0	0.0
			.debug_loc	33340	33340	0	0.0
			.debug_loclists	1506147	1506147	0	0.0
			.debug_ranges	4984	4984	0	0.0
			.debug_rnglists	96278	96278	0	0.0
			.debug_str	3059490	3059490	0	0.0
			.ramVecs	780	780	0	0.0
			.resetVecs	64	64	0	0.0
			.rodata	104250	104250	0	0.0
			.shstrtab	265	265	0	0.0
			.stack	2048	2048	0	0.0
			.strtab	481887	481887	0	0.0
			.symtab	287248	287248	0	0.0
			.text	496340	496340	0	0.0

[github-actions]

PR #26298: Size comparison from 77d72a8 to 7d43b3a

Full report (1 build for cc32xx)

platform	target	config	section	77d72a8	7d43b3a	change	% change
cc32xx	lock	CC3235SF_LAUNCHXL		0	0	0	0.0
			(read only)	602714	602714	0	0.0
			(read/write)	204156	204156	0	0.0
			.ARM.attributes	44	44	0	0.0
			.ARM.exidx	8	8	0	0.0
			.bss	197568	197568	0	0.0
			.comment	206	206	0	0.0
			.data	1468	1468	0	0.0
			.debug_abbrev	956984	956984	0	0.0
			.debug_aranges	103664	103664	0	0.0
			.debug_frame	350552	350552	0	0.0
			.debug_info	19521972	19521972	0	0.0
			.debug_line	2682751	2682751	0	0.0
			.debug_line_str	513	513	0	0.0
			.debug_loc	33340	33340	0	0.0
			.debug_loclists	1506147	1506147	0	0.0
			.debug_ranges	4984	4984	0	0.0
			.debug_rnglists	96278	96278	0	0.0
			.debug_str	3059490	3059490	0	0.0
			.ramVecs	780	780	0	0.0
			.resetVecs	64	64	0	0.0
			.rodata	104250	104250	0	0.0
			.shstrtab	265	265	0	0.0
			.stack	2048	2048	0	0.0
			.strtab	481887	481887	0	0.0
			.symtab	287248	287248	0	0.0
			.text	496340	496340	0	0.0

[github-actions]

PR #26298: Size comparison from 77d72a8 to 70168d3

Increases (1 build for mbed)

platform	target	config	section	77d72a8	70168d3	change	% change
mbed	lock-app	CY8CPROTO_062_4343W+release	(read/write)	2494568	2494888	320	0.0
			.text	1457252	1457572	320	0.0

Full report (1 build for mbed)

platform	target	config	section	77d72a8	70168d3	change	% change
mbed	lock-app	CY8CPROTO_062_4343W+release	(read only)	6224	6224	0	0.0
			(read/write)	2494568	2494888	320	0.0
			.bss	216296	216296	0	0.0
			.data	5144	5144	0	0.0
			.text	1457252	1457572	320	0.0