Add to local.conf or distro config the following to enable lto flavors
and lld linker

DISTRO_FEATURES += "thin-lto"
DISTRO_FEATURES += "full-lto"
DISTRO_FEATURES += "lld"

Add lto.bbclass

To enable LTO is currently per recipe, or globally

to enable globally add following to global config meta-data e.g.
local.conf

INHRIT += "lto"

other-wise enable LTO per recipe using

inherit lto to recipe via bbappend or in main recipe

Signed-off-by: Khem Raj <raj.khem@gmail.com>