wasi: add all _SC_* sysconf constants from wasi-libc#5030

surban wants to merge 1 commit intorust-lang:libc-0.2rust-lang/libc:libc-0.2from

rust-wasi-web:wasip1-sysconf-0.2rust-wasi-web/libc:wasip1-sysconf-0.2Copy head branch name to clipboard