Prevent child cargo process from messing with our stdin
Prevent child cargo process from messing with our stdin

By default, `spawn` inherits stderr/stdout/stderr of the parent
process, and so, if child, for example does fcntl(O_NONBLOCK), weird
stuff happens to us.

Closes https://github.com/rust-analyzer/lsp-server/pull/10

rust-analyzer/rust-analyzer,rust-analyzer/rust-analyzer,rust-analyzer/rust-analyzer,rust-analyzer/rust-analyzer,rust-analyzer/rust-analyzer