Windows stdio doesn't re-read GetStdHandle values

[alexcrichton]

Over time the value of GetStdHandle may change (e.g. see mozilla/sccache#80) and we should likely reload the value over time instead of caching the return value to catch cases like this.

[retep998]

There's very little value in caching the result. GetStdHandle takes 3 nanoseconds for me according to a quick bench.