Basic support for memory initialization checks for unions #7980

Job	Run time
benchcomp-tests	3m 50s
perf	28m 31s
regression (macos-13)	50m 19s
write-json-symtab-regression	16m 46s
regression (ubuntu-20.04)	27m 46s
regression (ubuntu-22.04)	30m 6s
documentation	2m 6s
regression (macos-14)	27m 16s
	3h 6m 40s

Provide feedback