tests: use statx instead of sendmmsg in has_function test #16658

Job	Run time
Arch Linux	20m 2s
Ubuntu Rolling (gcc, g++)	19m 30s
CUDA (on Arch)	7m 11s
Ubuntu Rolling (--unity=on -Ddefault_library=static, --no-unittests, gcc, g++)	13m 34s
Ubuntu Rolling (-Ddefault_library=both, --no-unittests, gcc, g++)	13m 35s
Fedora	19m 21s
Ubuntu Rolling (clang, clang++)	21m 56s
Gentoo	21m 23s
Arch / PyPy	19m 27s
Ubuntu Rolling (--unity=on, --no-unittests, clang, clang++)	15m 22s
OpenSUSE	16m 7s
Ubuntu Rolling (--cross ubuntu-armhf.json --cross linux-mingw-w64-64bit.json, 0, gcc, g++)	13m 27s
Ubuntu Bionic	14m 44s
Ubuntu Rolling (--cross ubuntu-armhf.json --cross linux-mingw-w64-64bit.json, --unity=on, gcc, g++)	13m 30s
	3h 49m 9s

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