metrowerks: Minor improvements #16667

Job	Run time
Arch Linux	11m 45s
Arch / PyPy	11m 45s
CUDA (on Arch)	7m 13s
Ubuntu Rolling (gcc, g++)	4m 24s
Fedora	11m 43s
Ubuntu Rolling (--unity=on -Ddefault_library=static, --no-unittests, gcc, g++)	10m 7s
Gentoo	11m 44s
Ubuntu Rolling (-Ddefault_library=both, --no-unittests, gcc, g++)	10m 14s
OpenSUSE	11m 43s
Ubuntu Rolling (clang, clang++)	5m 41s
Ubuntu Bionic	11m 44s
Ubuntu Rolling (--unity=on, --no-unittests, clang, clang++)	5m 47s
Ubuntu Rolling (--cross ubuntu-armhf.json --cross linux-mingw-w64-64bit.json, 0, gcc, g++)	10m 57s
Ubuntu Rolling (--cross ubuntu-armhf.json --cross linux-mingw-w64-64bit.json, --unity=on, gcc, g++)	11m 2s
	2h 15m 49s

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