RFR: 8315060: Out of tree incremental build fails with ccache

[Erik Joelsson]

On Fri, 25 Aug 2023 22:31:31 GMT, Erik Joelsson <erikj at openjdk.org> wrote:

> After [JDK-8313374](https://bugs.openjdk.org/browse/JDK-8313374), out of tree incremental builds with ccache started failing. The rewriting of the generated dependency (*.d) files creates object file paths with `/../` in them which make does not match to other rules. I don't think we should apply the rewriting when the build dir is outside CCACHE_BASEDIR. 
> 
> During review of [JDK-8313374](https://bugs.openjdk.org/browse/JDK-8313374) I also noted that the CCACHE_BASEDIR should point to WORKSPACE_ROOT rather than TOPDIR for ccache to work uniformly for OracleJDK and OpenJDK builds.
> 
> Both of these issues are addressed with this patch. I have tried various scenarios and it seems to be working for me, but would appreciate some more verification by people using ccache.

Thanks for reviews!

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PR Comment: https://git.openjdk.org/jdk/pull/15434#issuecomment-1696397652