multimedia/kvazaar: unbreak with clang on powerpc64

In file included from strategies/altivec/picture-altivec.c:24:
/usr/lib/clang/8.0.1/include/altivec.h:69:19: error: unknown type name 'vector'
static inline vector bool char __ATTRS_o_ai

^

/usr/lib/clang/8.0.1/include/altivec.h:69:26: error: expected identifier or '('
static inline vector bool char __ATTRS_o_ai

^

/usr/include/stdbool.h:39:14: note: expanded from macro 'bool'

^

[...]

PR: 240531
Submitted by: pkubaj