mpv: fix build on powerpc64 w/ altivec

Fixes
http://autobuild.buildroot.net/results/77f/77f00633b0b25f001cd4ca54ed3a12aee301c287



Add a patch to work around a name collision between bool and altivec's
bool apparent when using sdl2.

Signed-off-by: Sam Bobroff <sam.bobroff@au1.ibm.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>