RFR: 8251549: Update docs on building for Git

[Erik Joelsson]

On Mon, 26 Oct 2020 09:45:16 GMT, Magnus Ihse Bursie <ihse at openjdk.org> wrote:

>> BTW the value of coreautolf flag is asked during the installation of Git for windows, it is should be mentioned in the docs, since it is quite common issue.
>
> @jddarcy Recommended new wording:
> Suggestion:
> 
>       * Clone the JDK repository using the Cygwin command line `git` client
>         as instructed in this document.
> 
>         Using the Cygwin `git` client is the recommended way since it
>         guarantees that there will be no line ending issues and it works well
>         with other Cygwin tools. It is however also possible to use [Git for
>         Windows](https://gitforwindows.org). If you chose this path, make sure
>         to set `core.autocrlf` to `false` (this is asked during installation).

I would recommend putting in a link to the instructions on the Skara wiki page. They actually recommend Git for Windows and I have switched too. The main reason is to be able to use the token manager. To just clone and build, using Cygwin Git is definitely easier though.

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