WIP: test concatenation fix #418

Job	Run time
coverage / coverage	13m 28s
debug aarch64 / debug_aarch64	8m 1s
debug / debug	10m 56s
debug ASAN clang / debug_asan_clang	19m 31s
gcc centos 7 / default_gcc_centos_7	10m 34s
out of source / out_of_source	10m 52s
release / release	7m 54s
release ASAN clang / release_asan_clang	13m 58s
release clang / release_clang	7m 51s
release lto / release_lto	14m 52s
static build / static_build	6m 53s
release lto clang / release_lto_clang	15m 27s
	2h 20m 17s

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