Add "objects" support to Rust targets #17419

Job	Run time
Ubuntu Rolling (gcc, g++)	19m 50s
Ubuntu Rolling (--unity=on -Ddefault_library=static, --no-unittests, gcc, g++)	13m 39s
Ubuntu Rolling (-Ddefault_library=both, --no-unittests, gcc, g++)	13m 46s
Ubuntu Rolling (clang, clang++)	22m 53s
Arch / PyPy	20m 4s
Arch Linux	20m 7s
Ubuntu Rolling (--unity=on, --no-unittests, clang, clang++)	15m 25s
CUDA (on Arch)	7m 17s
Ubuntu Rolling (--cross ubuntu-armhf.json --cross linux-mingw-w64-64bit.json, 0, gcc, g++)	13m 43s
Fedora	17m 43s
Ubuntu Rolling (--cross ubuntu-armhf.json --cross linux-mingw-w64-64bit.json, --unity=on, gcc, g++)	13m 43s
Gentoo	22m 52s
OpenSUSE	16m 40s
Ubuntu Bionic	14m 50s
	3h 52m 32s

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