gcc: Fix building on ppc64le GCC 8 host

gcc: Fix building on ppc64le GCC 8 host

When building on a ppc64le host we see this error:

    build/genmatch --gimple ../../gcc/match.pd \
        > tmp-gimple-match.c
    ../../gcc/match.pd:120:1 error: expected (, got NAME
       negative value by 0 gives -0, not +0.  */

This was reported upstream[1] and fixed on the GCC 6 [2] and GCC 7 [3]
branches:

    Backport from mainline
    2018-01-10  Kelvin Nilsen  <kelvin@gcc.gnu.org>

    * lex.c (search_line_fast): Remove illegal coercion of an
    unaligned pointer value to vector pointer type and replace with
    use of __builtin_vec_vsx_ld () built-in function, which operates
    on unaligned pointer values.

The patches included in Buildroot contain just the code changes, and not
the changelog, to make it easer to manage backporting.

Tested on Ubuntu Cosmic ppc64le.

[1] https://gcc.gnu.org/bugzilla/show_bug.cgi?id=86162
[2] https://gcc.gnu.org/viewcvs/gcc?view=revision&revision=261621
[3] https://gcc.gnu.org/viewcvs/gcc?view=revision&revision=262243

Signed-off-by: Joel Stanley <joel@jms.id.au>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>