Set Windows console mode to enable support for ansi escape codes

Summary:
Windows console now supports supports ANSI escape codes, but we need to enable it using SetConsoleMode with ENABLE_VIRTUAL_TERMINAL_PROCESSING flag.

https://docs.microsoft.com/en-us/windows/console/console-virtual-terminal-sequences.

Syntax hightlighting now works fine on Windows:
https://i.imgur.com/P0i04A7.png

Reviewers: JDevlieghere, teemperor, zturner

Reviewed By: zturner

Subscribers: abidh, lldb-commits

Differential Revision: https://reviews.llvm.org/D51615

llvm-svn: 341497