fs: expose frsize field in statfs #4934

Job	Run time
Build slim tarball	2m 17s
x86_64-darwin: with shared libraries	33m 52s
x86_64-linux: with shared libraries	21m 56s
aarch64-darwin: with shared libraries	20m 10s
aarch64-linux: with shared libraries	18m 17s
	1h 36m 32s

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