lang/php81: fix build on powerpc64le

In file included from /wrkdirs/usr/ports/lang/php81/work/php-8.1.1/ext/hash/hash_xxhash.c:18:
In file included from ext/hash/php_hash_xxhash.h:21:
In file included from /wrkdirs/usr/ports/lang/php81/work/php-8.1.1/ext/hash/xxhash/xxhash.h:2412:
/usr/lib/clang/11.0.1/include/altivec.h:55:19: error: unknown type name 'vector'
static inline vector bool char __ATTRS_o_ai

^

/usr/lib/clang/11.0.1/include/altivec.h:56:10: error: unknown type name 'vector'
vec_perm(vector bool char a, vector bool char b, vector unsigned char __c);

^

/usr/lib/clang/11.0.1/include/altivec.h:56:32: error: unknown type name 'vector'
vec_perm(vector bool char a, vector bool char b, vector unsigned char __c);

^

/usr/lib/clang/11.0.1/include/altivec.h:66:19: error: unknown type name 'vector'
static inline vector bool short __ATTRS_o_ai vec_perm(

Patch from https://github.com/Cyan4973/xxHash/pull/672