Bug #78687 MySQL 5.6.27 (GPL-2) build fails with: #error "Unsupported platform"

Description:
Hello. I am currently running the GPL-2 licensed version of
MySQL, version 5.6.26, and have been able to compile and run MySQL 5.6 from source for all previous releases through this version. I should state up front that I have been running the database on an Apple PowerBook G4 with OS X 10.5.8 (Leopard). Unfortunately, I have not been able to build MySQL 5.6.27. Failure occurs about 25% of the way through the build. The build log contains the following message:

/mp2/local/var/macports/build/_mp2_local_var_macports_sources_rsync.macports.org_release_tarballs_ports_databases_mysql56/mysql56/work/mysql-5.6.27/storage/innobase/include/os0sync.h:504:4: error: #error "Unsupported platform"

and a few lines later:

:info:build /mp2/local/var/macports/build/_mp2_local_var_macports_sources_rsync.macports.org_release_tarballs_ports_databases_mysql56/mysql56/work/mysql-5.6.27/storage/innobase/include/sync0sync.ic:112: error: "os_atomic_clear" was not declared in this scope

Is MySQL still interested in supporting old Apple PPCs running OS X 10.5? If so, is there a designated place to send the full build log and work with a developer to fix this particular build? Any information would be greatly appreciated.  

I will attach the build log.

How to repeat:
To repeat, build MySQL 5.6.27 on a PowerBook G4 running OS X 10.5.8 (Leopard).  The failure occurs about 23% of the way into the build.

MySQL 5.6.17 build log

Attachment: main.log (application/octet-stream, text), 525.92 KiB.

Note: I am using MacPorts as a package manager, with base directory /mp2/local/ .

regression of this commit  to fix Bug #76135  ?

https://github.com/mysql/mysql-server/commit/f59d68eeae37338d7b25f2571407e763fa897e15

I can confirm that this issue breaks the build of mysql 5.5.46 for the following platforms:
- ppc
- ppc64
- s390
- s390x
- ia64

I expect the same result for mysql 5.6.27 too.

Is there any ETA on solving this issue? Thank you for any response.

Please check with latest releases.

No feedback was provided for this bug for over a month, so it is
being suspended automatically. If you are able to provide the
information that was originally requested, please do so and change
the status of the bug back to "Open".

See https://trac.macports.org/ticket/60400#comment:1 -- the "unsupported platform" error was still being observed with 5.6.47 on Mac OS X 10.5 PowerPC.

I am aware that MySQL 5.6 is unsupported on macOS as of 2018.

MacPorts has resolved the issue by using a compiler with proper atomic operation support, which excludes the older GCC-based compilers provided by Xcode for PowerPC Macs.