This adjusts the standard library test suite to mostly pass on Windows.
The remaining failures are due to various cases:
- memory corruption (`_swift_stdlib_free` in swiftDemangle)
- heap corruption (canGrowUsingRealloc)
- withVAList failure (unresolved)
- unicode handling on the command line
When working with Error types with unsigned raw values, numeric-cast into
a UInt and then map the bits over to an Int so we preserve values not
representable in an Int without wrapping.
Thanks to @jrose-apple for pointing this out!
From the Swift documentation:
"If you define an optional variable without providing a default value,
the variable is automatically set to nil for you."
