audio/sfizz: fix build on powerpc*

ori 0,0,0 is nop instruction on powerpc*
Additional headers are necessary:
In file included from /wrkdirs/usr/ports/audio/sfizz/work/sfizz-0.4.0/external/abseil-cpp/absl/base/internal/unscaledcycleclock.cc:27:
/usr/include/sys/sysctl.h:1185:25: error: unknown type name 'u_int'
int sysctl(const int *, u_int, void *, size_t *, const void *, size_t);

^

/wrkdirs/usr/ports/audio/sfizz/work/sfizz-0.4.0/external/abseil-cpp/absl/base/internal/unscaledcycleclock.cc:91:10: error: unknown type name 'once_flag'

static once_flag init_timebase_frequency_once;
       ^

/wrkdirs/usr/ports/audio/sfizz/work/sfizz-0.4.0/external/abseil-cpp/absl/base/internal/unscaledcycleclock.cc:93:18: error: no member named 'LowLevelCallOnce' in namespace 'absl::lts_2020_02_25::base_internal'

base_internal::LowLevelCallOnce(&init_timebase_frequency_once, [&]() {