Change a return back to an _exit(1). It's not different functionally … #1521

Job	Run time
test-linux-add_subdirectory (On)	28s
test-linux-add_subdirectory (Off)	55s
test-linux-fetchcontent (On)	32s
test-linux-findpackage (On)	17s
test-linux-fetchcontent (Off)	1m 37s
test-linux-findpackage (Off)	20s
test-macos-add_subdirectory (On)	30s
test-macos-add_subdirectory (Off)	40s
test-macos-fetchcontent (On)	31s
test-macos-findpackage (On)	26s
test-macos-fetchcontent (Off)	34s
test-macos-findpackage (Off)	23s
test-mingw-add_subdirectory (On)	2m 3s
test-mingw-add_subdirectory (Off)	3m 5s
test-mingw-fetchcontent (On)	1m 58s
test-mingw-findpackage (On)	1m 23s
test-windows-add_subdirectory (On)	1m 7s
test-mingw-findpackage (Off)	1m 11s
test-windows-add_subdirectory (Off)	1m 4s
test-mingw-fetchcontent (Off)	1m 59s
test-windows-fetchcontent (On)	1m 28s
test-windows-findpackage (On)	1m 24s
test-windows-fetchcontent (Off)	1m 37s
test-windows-findpackage (Off)	1m 30s
	27m 2s

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