LTOize: overriding flag‐o‐matic.eclass

A number of packages call strip-flags, replace-flags, filter-flags, and append-flags to manipulate the *FLAGS variables. LTOize has an experimental USE flag override-flagomatic to override these functions globally to turn these functions into no-ops. override-flagomatic is disabled by default. Users who use this functionality should report breakages as issues, so they can be manually resolved. To enable flag-o-matic for a package, set the variable LTO_ENABLE_FLAGOMATIC=yes for that package in package.cflags.

The relevant issue for this work is #57. Any ideas/suggestions, please post!