[jdk11u-dev] RFR: 8280863: Update build README to reflect that MSYS2 is supported [v2]

[George Adams]

> The only diffs are the supported VS versions and the fact that for JDK11u we state that versions older than VS 2017 are likely to be unsupported at some point.

George Adams has updated the pull request incrementally with one additional commit since the last revision:

  revert

-------------

Changes:
  - all: https://git.openjdk.org/jdk11u-dev/pull/1552/files
  - new: https://git.openjdk.org/jdk11u-dev/pull/1552/files/ee9e6d25..21f97ea3

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk11u-dev&pr=1552&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk11u-dev&pr=1552&range=00-01

  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk11u-dev/pull/1552.diff
  Fetch: git fetch https://git.openjdk.org/jdk11u-dev pull/1552/head:pull/1552

PR: https://git.openjdk.org/jdk11u-dev/pull/1552