Fix for issue #386 to enable LTO support.

[daniel-starke]

This pull request adds support for the gcc/g++ -flto flag by using the plugin enabled versions of ar and ranlib. This does not include the -flto flag by default. toolchain-gccarmnoneeabi 1.70201.0 seems to fail at linking stage when using LTO in some cases. A newer toolchain like 1.90201.191206 should be used instead when compiling with LTO.

[dzarda]

Is there a reason this cannot be merged ❓

[valeros]

Hi @daniel-starke ! Sorry for the late reply. Just to clarify, are there any possible side effects with enabled LTO on older toolchains like 1.70201.0 when gcc-ar and gcc-ranlib are used?

[daniel-starke]

Like mentioned in the commit, this patch does only enable support for LTO. It does not enable LTO itself. LTO comes with various constraints that can break existing code if not handled correctly. It can, after applying this patch, be enabled via command-line option -flto. However, I advice that everyone uses it on his/her own risk. But as it stands today, this feature is not usable at all with PlatformIO. The here proposed fix closes this gap, allowing everyone to add LTO compatibility to their work.

Just replacing ar with gcc-ar and ranlib with gcc-ranlib has no side effect, as far as I know.

[valeros]

Thanks!