Similar to BZ#19387 and BZ#20971, both i686 memchr optimized assembly
implementations (memchr-sse2-bsf and memchr-sse2) do not handle the
size overflow correctly.
It is shown by the new tests added by commit 3daef2c8ee4df29, where
both implementation fails with size as SIZE_MAX.
This patch uses a similar strategy used on 3daef2c8ee4df2, where
saturared math is used for overflow case.
Checked on i686-linux-gnu.
[BZ #21014]
* sysdeps/i386/i686/multiarch/memchr-sse2-bsf.S (MEMCHR): Avoid overflow
in pointer addition.
* sysdeps/i386/i686/multiarch/memchr-sse2.S (MEMCHR): Likewise.
23d27709a4