update cflags for unittest #319

Job	Run time
build (ubuntu-latest, Debug, gcc)	1m 43s
build (ubuntu-latest, Debug, clang)	1m 52s
build (windows-latest, Release, cl)	2m 59s
build (ubuntu-latest, Release, gcc)	2m 53s
build (windows-latest, Debug, cl)	2m 28s
build (macos-latest, Debug, clang)	59s
build (macos-latest, Release, clang)	1m 19s
build (ubuntu-latest, Release, clang)	2m 29s
	16m 42s

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