The native pkg doesn't need the TOOLCHAIN_OPTIONS, but it maybe used by native pkgs, for example:
The cmake.bbclass uses TOOLCHAIN_OPTIONS:
OECMAKE_C_FLAGS ?= "${HOST_CC_ARCH} ${TOOLCHAIN_OPTIONS} ${CPPFLAGS}"

and TOOLCHAIN_OPTIONS is:
TOOLCHAIN_OPTIONS = " --sysroot=${STAGING_DIR_TARGET}"

If a native pkg inherits cmake.bbclass, then:
TOOLCHAIN_OPTIONS = " --sysroot="

and OECMAKE_C_FLAGS would be:
${HOST_CC_ARCH} --sysroot= ${CPPFLAGS}

This would cause unexpected errors, I think that we can make TOOLCHAIN_OPTIONS empty
in native.bbclass since native pkgs doesn't need it.