RFR: 8313374: --enable-ccache's CCACHE_BASEDIR breaks builds [v2]

[Jan Kratochvil]

On Mon, 31 Jul 2023 04:40:58 GMT, Jan Kratochvil <jkratochvil at openjdk.org> wrote:

>> https://bugs.openjdk.org/browse/JDK-8313374
>> --enable-ccache's CCACHE_BASEDIR breaks builds
>
> Jan Kratochvil has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Try not to remove CCACHE_BASEDIR.

OK so the real problem is:
- OpenJDK makefiles operate with absolute paths to the target objects files.
- Dependency files (`*.d`) switch to relative paths to everything by turning on `CCACHE_BASEDIR`.
- `make` does not find a relative vs. absolute filename of the target to be the same as `make` does just a string comparison, not filesystem inode comparison.

When trying to fix it I have found `$(FILE_MACRO_CFLAGS)` is on my system `-fmacro-prefix-map=/home/user/jdk-src-dir/=`. I do not see why it was implemented this way by JDK-8226346 (and I cannot see this Bug). So I have removed it.

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PR Comment: https://git.openjdk.org/jdk/pull/15080#issuecomment-1657564778