cargo: Add support for target specific dependencies #16766

Job	Run time
Arch / PyPy	19m 50s
Arch Linux	20m 14s
Ubuntu Rolling (gcc, g++)	19m 46s
Ubuntu Rolling (--unity=on -Ddefault_library=static, --no-unittests, gcc, g++)	13m 34s
CUDA (on Arch)	7m 51s
Ubuntu Rolling (-Ddefault_library=both, --no-unittests, gcc, g++)	14m 1s
Fedora	19m 50s
Ubuntu Rolling (clang, clang++)	22m 14s
Ubuntu Rolling (--unity=on, --no-unittests, clang, clang++)	15m 9s
Gentoo	22m 28s
Ubuntu Rolling (--cross ubuntu-armhf.json --cross linux-mingw-w64-64bit.json, 0, gcc, g++)	14m 27s
OpenSUSE	15m 57s
Ubuntu Rolling (--cross ubuntu-armhf.json --cross linux-mingw-w64-64bit.json, --unity=on, gcc, g++)	14m 3s
Ubuntu Bionic	14m 55s
	3h 54m 19s

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