RFR: 8273072: Avoid using += in configure [v3]

[Jie Fu]

On Fri, 27 Aug 2021 13:53:56 GMT, Magnus Ihse Bursie <ihse at openjdk.org> wrote:

>> JDK-8272700 was created to fix a bug in a variable assignment in configure. While it fixed the bug, it kept the problematic syntax that caused the bug in the first place. 
>> 
>> We do not use the `FOO+="appended"` syntax for appending to variables in shell scripts, since this differs from what you'd expect (and what make produces) in that no space is added before the appended text. 
>> 
>> Instead, we use the longer, but clearer `FOO="$FOO appended"`.
>
> Magnus Ihse Bursie has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Fix copyright year and remove space

Marked as reviewed by jiefu (Reviewer).

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PR: https://git.openjdk.java.net/jdk/pull/5276