Remove some `hasattr` checks from Compilers #16692

Job	Run time
Arch Linux	20m 27s
CUDA (on Arch)	7m 58s
Fedora	20m 11s
Arch / PyPy	19m 29s
Gentoo	21m 47s
OpenSUSE	16m 40s
Ubuntu Bionic	15m 23s
Ubuntu Rolling (gcc, g++)	19m 56s
Ubuntu Rolling (--unity=on -Ddefault_library=static, --no-unittests, gcc, g++)	14m 1s
Ubuntu Rolling (-Ddefault_library=both, --no-unittests, gcc, g++)	14m 6s
Ubuntu Rolling (clang, clang++)	26m 10s
Ubuntu Rolling (--unity=on, --no-unittests, clang, clang++)	15m 45s
Ubuntu Rolling (--cross ubuntu-armhf.json --cross linux-mingw-w64-64bit.json, 0, gcc, g++)	14m 3s
Ubuntu Rolling (--cross ubuntu-armhf.json --cross linux-mingw-w64-64bit.json, --unity=on, gcc, g++)	13m 35s
	3h 59m 31s

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