build

Update libstd example to include -Zfmt-debug #144

Job	Run time
Default (ubuntu-latest, stable)	13s
no_main-win (stable)	48s
Default (ubuntu-latest, nightly)	13s
build-std (build_std)	42s
no_main-win (nightly)	25s
no_std (ubuntu-latest, stable)	11s
Default (macos-latest, stable)	17s
build-std (no_main/nix)	44s
no_std (ubuntu-latest, nightly)	11s
Default (macos-latest, nightly)	17s
no_std (macos-latest, stable)	16s
Default (windows-latest, stable)	55s
no_std (macos-latest, nightly)	15s
no_std-win (stable)	47s
Default (windows-latest, nightly)	41s
no_std-win (nightly)	23s
	7m 18s

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