RFR: 8328106: COMPARE_BUILD improvements

[Erik Joelsson]

On Wed, 13 Mar 2024 15:48:15 GMT, Magnus Ihse Bursie <ihse at openjdk.org> wrote:

> This is a collection of various improvements to `COMPARE_BUILD` I have been using lately.
> 
> * Introducing `DEBUG_CDS_ARCHIVE` make variable, which is set automatically when using `COMPARE_BUILD`. This will create a detailed log file for the `classes*.jsa` CDS archives creation, to help debug any differences in these files. It is also possible to call `make DEBUG_CDS_ARCHIVE=true` to get this functionality even without running comparisons.
> 
> * `otool` on macOS did not include all relevant information.
> 
> * We now create modern "unified" diffs using `diff -u` whenever the output is supposed to be seen by the user. For diffs that are processed by the tooling, the traditional style `>`/`<` diffs are still used.
> 
> * "Other" files are now getting symlinks as well, to facilitate debugging; and also the diff output is improved.
> 
> * Better handling of showing diffs: 
> 
>   The `-vv` argument was too verbose. To see diffs, you also were required to see redundant information about unchanged files, which spammed the log.  Now instead you can set `--diffs` to see the diffs but not unchanged files. By default, this is cut after 500 lines, but using `--diffs=full` you can get the whole diffs. Beware that this can cause logs the size of hundereds of MB!
> 
>   Now `-vv` is aliased to `-v --diffs`, and `COMPARE_BUILD` is run with `--diffs` instead of `-vv` as default.
> 
> * And finally, for some reason (merge error?) the file `compare_exceptions.sh.incl` were not properly removed before, just replaced with an emty file. This is now fixed.

Marked as reviewed by erikj (Reviewer).

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

PR Review: https://git.openjdk.org/jdk/pull/18279#pullrequestreview-1934689315