gcc: Handle uclibc linker relocation for multilib support

We need to handle the UCLIBC_* linker variables in the same way
as we do the GLIBC_* ones to allow uclibc multilib to work properly.

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
attr: Fix uclibc builds

attr needs libintl headers and libs. Add in the missing dependency and
ensure the linker flag gets passed in multilib builds by replacing the
PN == BPN check with a class-target override instead.

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