Odin explicitly builds using `clang++` regardless of toolchain. Older
Odin ebuilds explicitly cleared `CPPFLAGS` and `CXXFLAGS` with the
comment "build_odin.sh sets its own flags. Some gcc flags cause build
failures"; this stripping was later migrated to `strip-flags`.
Full stripping isn't necessary, though: the Odin build script _appends_
its own flags instead of replacing them, and GCC-specific flags can be
stripped using `strip-unsupported-flags` instead.
Closes: https://bugs.gentoo.org/974732
Signed-off-by: Itai Ferber <itai@itaiferber.net>
