i686: Fix build with --disable-multiarch

Since i686 provides the fortified wrappers for memcpy, mempcpy,
memmove, and memset on the same string implementation, the static
build tries to optimized it by not tying the fortified wrappers
to string routine (to avoid pulling the fortify function if
they are not required).

Checked on i686-linux-gnu building with different option:
default and --disable-multi-arch plus default, --disable-default-pie,
--enable-fortify-source={2,3}, and --enable-fortify-source={2,3}
with --disable-default-pie.
Reviewed-by: Siddhesh Poyarekar <siddhesh@sourceware.org>