build

Add support for Windows `#![no_main]` #108

Job	Run time
no_std_win (stable)	49s
build-std (build_std)	45s
build-std (no_main/nix)	44s
Default (ubuntu-latest, stable)	11s
Default (ubuntu-latest, nightly)	13s
no_std_win (nightly)	30s
Default (macos-latest, stable)	21s
no_std (ubuntu-latest, stable)	16s
Default (macos-latest, nightly)	28s
no_std (ubuntu-latest, nightly)	11s
Default (windows-latest, stable)	55s
no_std (macos-latest, stable)	10s
Default (windows-latest, nightly)	26s
no_std (macos-latest, nightly)	19s
	6m 18s

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