Patches for LTO in the clang toolchain

[markyang92]

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This is a patch for LTO support in clang within yoe-distro.
You can test LTO in yoe-distro on an rpi4-64 environment with the following settings.

# yoe-distro/conf/local.conf
require conf/distro/include/lto.inc
DISTRO_FEATURES:append = " lto"
# or thin-lto
# DISTRO_FEATURES:append = " lto thin-lto"

I performed a build test with the following command.

$ bitbake yoe-simple-image

• The most severe problem currently seems to be recipes that force the bfd linker while using the clang toolchain.
  In yoe-simple-image, only bluez5, systemd-boot, and zlib are forced to use the bfd linker while using the clang Toolchain.
  Whether it's thin-lto or lto, when using the clang toolchain, the lld linker is recommended.
  If using the bfd linker, the LLVMgold.so plugin is required. This requires the gold linker.

However, the gold linker has been deprecated.

For now, the clang+bfd recipe has been avoided by setting LTO = "", but further consideration is needed.