RFR: 8344607: Link Time Optimization - basic support for clang

[Matthias Baesken]

Support the clang toolchain when link time optimization is configured.
Please note that this is NOT intended to enable lto by default and NOT to fix all possible clang-supporting builds or test issues .

It works on my Linux x86_64 SUSE 15 test machine with  clang15.0.7, also on macOS with Xcode 13.1 devkit  and Xcode 15.4 .

To be able to build on macOS with Xcode, I had to deal with one issue.  The lto-link process runs into this error 


ld: <inline asm>:11:1: symbol 'SpinPause_return' is already defined
SpinPause_return:        
^
for architecture arm64
clang: error: linker command failed with exit code 1 (use -v to see invocation)


Seems that when building with LTO,  the  inline assembler code in SpinPause() is not handled well. In the lto inlining the label  SpinPause_return is generated multiple times and causes an 'already defined' error. This goes away when adding NOINLINE to this function.
Linux/clang did not show this issue, probably the toolchain there does not have the error.

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Commit messages:
 - JDK-8344607

Changes: https://git.openjdk.org/jdk/pull/22412/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=22412&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8344607
  Stats: 5 lines in 2 files changed: 5 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/22412.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/22412/head:pull/22412

PR: https://git.openjdk.org/jdk/pull/22412