multilib_header: recognize BPF as a target
When building with `clang -target bpf` using the
multilib_header, a recursion was unavoidable because
bits/wordsize.h would #include itself, still lacking
a definition for __MHWORDSIZE or __WORDSIZE.
(From OE-Core rev: 70b41b3c335a80b4ac243f468f22331d261299db)
Signed-off-by: Daniel Díaz <daniel.diaz@linaro.org>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>