linux

Add start-group/end-group flags when linking a program with rustc #17414

Job	Run time
Arch / PyPy	20m 12s
Arch Linux	20m 16s
CUDA (on Arch)	7m 3s
Fedora	17m 41s
Ubuntu Rolling (gcc, g++)	19m 15s
Gentoo	22m 19s
Ubuntu Rolling (--unity=on -Ddefault_library=static, --no-unittests, gcc, g++)	13m 32s
Ubuntu Rolling (-Ddefault_library=both, --no-unittests, gcc, g++)	14m 2s
Ubuntu Rolling (clang, clang++)	22m 56s
Ubuntu Rolling (--unity=on, --no-unittests, clang, clang++)	15m 43s
OpenSUSE	16m 33s
Ubuntu Rolling (--cross ubuntu-armhf.json --cross linux-mingw-w64-64bit.json, 0, gcc, g++)	13m 47s
Ubuntu Bionic	14m 59s
Ubuntu Rolling (--cross ubuntu-armhf.json --cross linux-mingw-w64-64bit.json, --unity=on, gcc, g++)	13m 22s
	3h 51m 40s

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