RFR: 8345265: Minor improvements for LTO across all compilers [v6]

[Julian Waters]

> This is a general cleanup and improvement of LTO, as well as a quick fix to remove a workaround in the Makefiles that disabled LTO for g1ParScanThreadState.cpp due to the old poisoning mechanism causing trouble. The -Wno-attribute-warning change here can be removed once Kim's new poisoning solution is integrated.
> 
> - -fno-omit-frame-pointer is added to gcc to stop the linker from emitting code without the frame pointer
> - -flto is set to $(JOBS) instead of auto to better match what the user requested
> - -Gy is passed to the Microsoft compiler. This does not fully fix LTO under Microsoft, but prevents warnings about -LTCG:INCREMENTAL at least

Julian Waters has updated the pull request incrementally with one additional commit since the last revision:

  Revert LINK_TIME_OPTIMIZATION in ClientLibraries.gmk

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Changes:
  - all: https://git.openjdk.org/jdk/pull/22464/files
  - new: https://git.openjdk.org/jdk/pull/22464/files/fbe79af6..3e6c0650

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=22464&range=05
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=22464&range=04-05

  Stats: 1 line in 1 file changed: 0 ins; 1 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/22464.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/22464/head:pull/22464

PR: https://git.openjdk.org/jdk/pull/22464