RFR: build: update to JDK 15.0.1 [v2]

[Robin Westberg]

On Mon, 14 Dec 2020 11:45:10 GMT, Erik Helin <ehelin at openjdk.org> wrote:

>> Hi all,
>> 
>> please review this patch that updates the JDK used for building Skara to 15.0.1.
>> 
>> Testing:
>> - [x] `make images`
>> - [x] `make test`
>> 
>> Thanks,
>> Erik
>
> Erik Helin has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Use explicit newline pattern

Looks good, I guess an alternative would have been to simply disable the tests on Windows and hope that \R becomes usable again in the future. But this works too. :)

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Marked as reviewed by rwestberg (Reviewer).

PR: https://git.openjdk.java.net/skara/pull/969