RFR: 8251549: Update docs on building for Git

[Michael Keck]

On Tue, 3 Nov 2020 11:41:20 GMT, Magnus Ihse Bursie <ihse at openjdk.org> wrote:

>> 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.
>
> @erikj79 
> 
> Ok, here is a completely rewritten portion, which highlights the differences between Cygwin git and Git for Windows.
> 
> Suggestion:
> 
>       * You need to install a git client. You have two choices, Cygwin git or
>         Git for Windows. Unfortunately there are pros and cons with each choice.
> 
>         * The Cygwin `git` client has no line ending issues and understands
>           Cygwin paths (which are used throughout the JDK build system).
>           However, it does not currently work well with the Skara CLI tooling.
>           Please see the [Skara wiki on Git clients](
>           https://wiki.openjdk.java.net/display/SKARA/Skara#Skara-Git) for
>           up-to-date information about the Skara git client support.
> 
>         * The [Git for Windows](https://gitforwindows.org) client has issues
>           with line endings, and do not understand Cygwin paths. It does work
>           well with the Skara CLI tooling, however. To alleviate the line ending
>           problems, make sure you set `core.autocrlf` to `false` (this is asked
>           during installation).
> 
> @jddarcy Do you find this acceptable? This PR has been open for almost a month, and it's starting getting embarrassing that our build instruction does not match the new Github reality. :(

You should add a `.gitattributes` file which defines the desired line endings for each file type or for all files. Recommending a specific git client just because of that (?) is unnecessary.

Here is a arbitrary example:
https://github.com/alexkaratarakis/gitattributes/blob/f017637f08305dd1402fd025f6b648c45f04f499/Common.gitattributes#L49

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