RFR: 8320763: Fix spacing arround assignment in spec.gmk.in [v2]

[Iris Clark]

On Mon, 27 Nov 2023 15:05:20 GMT, Magnus Ihse Bursie <ihse at openjdk.org> wrote:

>> For some reason, we have not been consistent with using spaces around the assignment operators (`:=` and `=`) in spec.gmk.in. This has annoyed me for a long time.
>> 
>> When making this change, I noticed that there are a lot of late evaluation assignments (= instead of :=) that should not be there. To not confuse the code review, I will fix these separately. Thus this change will only change whitespace.
>
> Magnus Ihse Bursie has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Fix ?=

Marked as reviewed by iris (Reviewer).

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PR Review: https://git.openjdk.org/jdk/pull/16825#pullrequestreview-1750990335