New diagnostic formatter adds extra whitespace on Windows

[bnbarham]

Description

The new formatter on Windows seems to add extra whitespace between each line:

=== .../swift/stdlib/public/core/Macros.swift:32:11 ===

31 | public macro fileID<T: ExpressibleByStringLiteral>() -> T =

32 |   Builtin.FileIDMacro

   |           ^ warning: ignoring definition of unknown builtin macro 'FileIDMacro'

33 |

Possibly some mishandling of \r\n?

Steps to Reproduce

Run a swift build on Windows now that it uses the new formatter by default for the compiler compilation. CC @compn

[ahoppen]

rdar://106434712

[compnerd]

This is almost certainly in the C++ implementation and not in the Swift implementation. Should we move this to the Swift repository?