dav1d: Make |needs_stack_alignment| work with GCC

Right now, building dav1d with GCC fails with

    gcc: error: unrecognized command line option ‘-mstack-alignment=32’; did you mean ‘-fipa-cp-alignment’?

Follow third_party/dav1d/meson.build and pass the right flags for
GCC (-mpreferred-stack-boundary and -mincoming-stack-boundary instead of
-mstack-alignment and -mstackrealign, respectively).

Bug: 819294
Change-Id: Ie735780e49bb53921ebabb1ab66186ebe2353cf2
Reviewed-on: https://chromium-review.googlesource.com/c/1473272
Commit-Queue: Raphael Kubo da Costa <raphael.kubo.da.costa@intel.com>
Auto-Submit: Raphael Kubo da Costa <raphael.kubo.da.costa@intel.com>
Reviewed-by: Dale Curtis <dalecurtis@chromium.org>
Cr-Commit-Position: refs/heads/master@{#632573}
1 file changed