RFR: 8345265: Minor improvements for LTO across all compilers [v2]

[Kim Barrett]

On Thu, 9 Jan 2025 16:06:17 GMT, Matthias Baesken <mbaesken at openjdk.org> wrote:

> Hi, the workaround 'disable lto in g1ParScanThreadState because of special inlining/flattening used there' is removed , why this works now ?

The issue there was the `-Wattribute-warning` warnings that were being generated.  But this change is suppressing
those warnings in the LTO link:
https://github.com/openjdk/jdk/blame/9d05cb8eff344fea3c6b9a9686b728ec53963978/make/hotspot/lib/JvmFeatures.gmk#L176C11-L176C11
Note that won't work with the new portable forbidding mechanism based on `deprecated` attributes.

I'm trying this new version, and I still get a few other warnings and then seem to have a process hang in lto1-ltrans.
The switch from `-flto=auto` to `-flto=$(JOBS)` doesn't seem to have helped in that respect.

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PR Comment: https://git.openjdk.org/jdk/pull/22464#issuecomment-2581673261