RFR: 8255526: Enable jcheck whitespace checking of build system files [v2]

[Magnus Ihse Bursie]

On Thu, 29 Oct 2020 00:54:41 GMT, Magnus Ihse Bursie <ihse at openjdk.org> wrote:

>> I need to put this on hold for a while. It turned out that the Skara jcheck disallows initial tabs, which makes sense for sane source code formats (java, c++) but is unfortunately an incorrect assumption for makefiles.
>> 
>> (I tested that the modification to jcheck detected trailing whitespaces, but it never occurred to me that I needed to modify a line starting with tab to show that this fix would not work...)
>
> Fix for Skara in PR https://github.com/openjdk/skara/pull/929.

Now the Skara fix is deployed, and I've added instructions to the jcheck configure file to allow tabs in Makefiles, so this is finally ready to be integrated.

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PR: https://git.openjdk.java.net/jdk/pull/898