Add `version.h` defining `WASI_LIBC_VERSION` #1255

Job	Run time
Rustfmt	13s
wasi-headers test	0s
Build libc (ubuntu-latest, 10.0.0)	1m 10s
Build libc (macos-latest, 10.0.0)	2m 36s
Build libc (windows-latest, 10.0.0)	2m 45s
Build libc (ubuntu-latest, 16.0.0, x86_64-linux-gnu-ubuntu-18.04)	2m 40s
Build libc (macos-latest, 15.0.7, x86_64-apple-darwin21.0)	4m 35s
Build libc (windows-latest, 16.0.0)	4m 11s
	18m 10s

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