Use GuardedInstruction for cfg_t node, instead of basic_block #1454

Job	Run time
build_windows (Debug, tests)	44m 1s
build_ubuntu (Debug, tests)	32m 38s
build_windows (Debug, library)	4m 36s
build_ubuntu (Debug, library)	1m 9s
build_windows (Release, tests)	10m 34s
build_ubuntu (Release, tests)	6m 27s
build_windows (Release, library)	4m 38s
build_ubuntu (Release, library)	1m 12s
	1h 45m 15s

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