mulitilib_header: Avoid sstate checksum issues for -native recipes

mulitilib_header: Avoid sstate checksum issues for -native recipes

The use of arch specific variables like MIPSPKGSFX_ABI was creeping
into the -native sstate checksums of package like ncurses-native.

This is pointless and undesireable. We could add specific variable
exclusions but we might as well just brute force the code to be disabled
in the -native case since we don't use multilibs in the native case.

[YOCTO #3827]

(From OE-Core rev: cc7352ed990b1bdd26203a4d3b21286280ac26c5)

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>