add stubs for `statvfs`, `chmod`, etc. #1078

Job	Run time
Rustfmt	7s
wasi-headers test	0s
Build libc (ubuntu-latest, 10.0.0)	1m 12s
Build libc (macos-latest, 10.0.0)	2m 5s
Build libc (windows-latest, 10.0.0)	2m 15s
Build libc (ubuntu-latest, 16.0.0, x86_64-linux-gnu-ubuntu-18.04)	2m 19s
Build libc (macos-latest, 15.0.7, x86_64-apple-darwin21.0)	2m 49s
Build libc (windows-latest, 16.0.0)	3m 26s
	14m 13s

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