RFR: 8251549: Update docs on building for Git

Mon Sep 7 07:25:06 UTC 2020

On Sat, 5 Sep 2020 20:13:18 GMT, Joe Darcy <darcy at openjdk.org> wrote:

> 8251549: Update docs on building for Git

Overall looks  good, but please restore the recommendation to stick with Cygwin tools.

doc/building.md line 92:

> 90:         spaces and/or mixed upper and lower case letters.
> 91:
> 92:       * Clone the JDK repository using [Git for Windows](https://gitforwindows.org).

I think I said before, this is *not* a recommended way! Instead, git from Cygwin is still recommended.

Git for Windows will for instance set the coreautolf flag. Now we have pushed a work-around for this, but I object
to *recommending* git for windows.

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Changes requested by ihse (Reviewer).

PR: https://git.openjdk.java.net/jdk/pull/21