git: openjdk/jdk11u-dev: 8280863: Update build README to reflect that MSYS2 is supported

Fri Nov 25 18:42:23 UTC 2022

Changeset: b5555c19
Author:    George Adams <gdams at openjdk.org>
Date:      2022-11-25 18:41:16 +0000
URL:       https://git.openjdk.org/jdk11u-dev/commit/b5555c191537c27e6b7dcf7ac15c4dfe2967688e

8280863: Update build README to reflect that MSYS2 is supported

Reviewed-by: clanger
Backport-of: 204e67a7adedc5ff8ed6dbe1da7aa1397c9beb38

! doc/building.html
! doc/building.md