These routines are not extensively used (gnulib documentation even
recommend use a replacement [1]), and there is already a POWER8
version that uses proper vectorized instructions.
[1] https://www.gnu.org/software/gnulib/manual/gnulib.html#C-strings
Checked with a build for some powerpc variations.
Reviewed-by: Peter Bergner <bergner@linux.ibm.com>