Use `const_error!` when possible
Replace usages of `io::Error::new(io::ErrorKind::Variant, "constant string")` with `io::const_error!(io::ErrorKind::Variant, "constant string")` to avoid allocations when possible. Additionally, fix `&&str` error messages in SGX and missing/misplaced trailing commas in `const_error!`.
c04801dbb9