Add `derive(Debug)` stub #8697

Job	Run time
build-and-check-asan	28m 25s
build-and-check-gcc-5	29m 36s
build-and-check-ubuntu-32bit	24m 20s
build-and-check-ubuntu-64bit	24m 27s
build-and-check-ubuntu-64bit-glibcxx	26m 58s
	2h 13m 46s

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