RFR: 8304893: Link Time Optimization with gcc can be faster [v3]

[David Holmes]

On Thu, 30 Mar 2023 23:38:12 GMT, Julian Waters <jwaters at openjdk.org> wrote:

>> A previous argument against link time optimization support that we have for gcc is that it was extremely slow. After some checks it turns out we are passing rather inefficient flags to gcc in optimized builds. Changing these flags to run the linker optimizations in parallel and passing additional flags to the compiler have the ability to speed this process up significantly. Also fixes some incorrect flags passed to ld for linking as well
>
> Julian Waters has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Flag should be used instead

Seems okay. Thanks.

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Marked as reviewed by dholmes (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/13180#pullrequestreview-1366335916