RFR: 8356657: Use stable source-date for cmp-baseline jib profiles

[Chen Liang]

On Fri, 9 May 2025 22:41:09 GMT, Mikael Vidstedt <mikael at openjdk.org> wrote:

> The cmp-baseline builds expect the source-date to be stable across the two builds (really: invocations of configure). For CI builds the source-date gets set based on information from the job, but for local builds it gets the default "current" value which will not be the same for the two builds.
> 
> While it's possible to override this on the command line it would be more user friendly to have jib provide a stable source-date instead.
> 
> Testing: tier1,builds-tier[2-5]

Let's fix our builds!

-------------

Marked as reviewed by liach (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/25160#pullrequestreview-2829846817