games/black-hole-solver: fix build on powerpc64le

Another namespace collision:
In file included from /wrkdirs/usr/ports/games/black-hole-solver/work/black-hole-solver-1.8.0/xxHash-wrapper/xxHash-0.7.2/xxh3.h:162:
/usr/lib/clang/11.0.0/include/altivec.h:55:19: error: unknown type name 'vector'
static inline vector bool char __ATTRS_o_ai