Use GuardedInstruction for cfg_t node, instead of basic_block #1455

Job	Run time
build_windows (Debug, tests)	43m 53s
build_windows (Debug, library)	3m 57s
build_windows (Release, tests)	10m 46s
build_ubuntu (Debug, tests)	33m 42s
build_windows (Release, library)	5m 18s
build_ubuntu (Debug, library)	1m 11s
build_ubuntu (Release, tests)	6m 43s
build_ubuntu (Release, library)	1m 10s
	1h 46m 40s

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