Add `DefinedMacros` handler #7395

Job	Run time
build test linux x86-64	3m 52s
build test windows x86-64	14m 53s
check-rust	1m 53s
scarb-metadata compatibility check	50s
doc tests	3m 10s
check-website	13s
test linux x86-64 1/8	16m 6s
test linux x86-64 2/8	16m 53s
test linux x86-64 3/8	15m 0s
test linux x86-64 4/8	12m 33s
test linux x86-64 5/8	12m 21s
test linux x86-64 6/8	9m 33s
test linux x86-64 7/8	9m 32s
test linux x86-64 8/8	10m 32s
test windows x86-64 1/8	13m 37s
test windows x86-64 2/8	17m 1s
test windows x86-64 3/8	13m 49s
test windows x86-64 4/8	13m 24s
test windows x86-64 5/8	11m 38s
test windows x86-64 6/8	8m 59s
test windows x86-64 7/8	8m 42s
test windows x86-64 8/8	10m 5s
	3h 44m 36s

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