wasi-libc should probably not define _POSIX_CPUTIME and _POSIX_THREAD_CPUTIME...

[whitequark]

... since it doesn't have CLOCK_PROCESS_CPUTIME_ID or CLOCK_THREAD_CPUTIME_ID.

I was compiling w2c2 to Wasm and discovered that it does not because of these lines: https://github.com/turbolent/w2c2/blob/22a9adeef081714e0d07ea62aa0ec734c6a5f99f/wasi/wasi.c#L2027-L2038

POSIX seems to pretty clearly indicate that the macros in the title indicate the presence of the clocks above, so wasi-libc should probably not define these macros.