The `os.exec()` function doesn't seem to support setting environment
variables in a subprocess. That is, its options parameter needs an `env`
option so something like this is possible:
const out = os.pipe();
const pid = os.exec(["/bin/sh", "-c", "echo $FOO"], {
block: false,
usePath: true,
stdout: out[1],
env: {
FOO: "Bar",
},
});
os.close(out[1]);
const stream = std.fdopen(out[0], "r");
console.log(stream.readAsString()); // Outputs "Bar"
