Upstream: Gentoo GCC LTO Linker Plugin Support

Binutils needs a way to obtain the LTO plugin from GCC in order to properly perform LTO and other linking tasks. Currently ld, ar, nm, and ranlib are known to use this plugin in LTO builds. There are two ways to do this: pass the path to the plugin manually to each of those utilities, or install a symlink to the plugin in binutils bfd_plugins directory and have binutils automatically load it. Support for automatically loading the LTO plugin from this directory was added in 2014 (thanks @pchome!). In this overlay, we choose the automatic approach because passing in the path manually (i.e., setting your AR, NM, and RANLIB variables to point to GCC wrappers) causes problems in legitimate cases, such as building toolchains. To facilitate this, Shane created a patch for gcc-config that creates this symlink for you, which thankfully has been merged upstream as of December 17 2017. Therefore, no action is required on the user's part -- sys-config/ltoize depends on a recent enough version of sys-devel/gcc-config that is guaranteed to have LTO linker plugin support.

(Thanks @rx80!) If you're interested in seeing where the symlink points, you can check it as follows (on amd64):

ls -l /usr/x86_64-pc-linux-gnu/binutils-bin/lib/bfd-plugins/liblto_plugin.so

This should point to your active GCC's liblto_plugin.so. For example, for GCC 10.1.0, it should look something like:

> ls /usr/libexec/gcc/x86_64-pc-linux-gnu/10.1.0/liblto_plugin.so -la
> lrwxrwxrwx 1 root root 22 Oct 13 09:17 /usr/libexec/gcc/x86_64-pc-linux-gnu/10.1.0/liblto_plugin.so -> liblto_plugin.so.0.0.0*