Fix test failures with gcc -O2 #589

Job	Run time
find_package/linux/Release	4m 30s
find_package/linux/Debug	2m 52s
find_package/linux/libcxx/Release	4m 10s
find_package/linux/libcxx/Debug	3m 5s
find_package/macos/Release	1s
find_package/macos/Debug	1s
find_package/win/Release	5m 29s
find_package/win/Debug	3m 48s
find_library/linux/Release	3m 58s
find_library/linux/Debug	2m 50s
find_library/linux/libcxx/Release	4m 24s
find_library/linux/libcxx/Debug	2m 48s
find_library/macos/Release	1s
find_library/macos/Debug	1s
find_library/win/Release	6m 24s
find_library/win/Debug	4m 31s
singleheader/linux/Release	4m 19s
singleheader/linux/Debug	3m 7s
singleheader/linux/libcxx/Release	5m 47s
singleheader/linux/libcxx/Debug	3m 25s
singleheader/macos/Release	1s
singleheader/macos/Debug	1s
singleheader/win/Release	5m 21s
singleheader/win/Debug	3m 40s
	1h 14m 34s

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