audio/jack: fix build on powerpc and powerpc64

Use GCC:
09:13:58 runner ['c++', '-O2', '-pipe', '-fPIC', '-fstack-protector-strong', '-fno-strict-aliasing', '-Wall', '-Wno-invalid-offsetof', '-std=gnu++11', '-fPIC', '-Ifreebsd', '-I../freebsd', '-Iposix', '-I../posix', '-Icommon', '-I../common', '-Icommon/jack', '-I../common/jack', '-I.', '-I..', '-I../compat/alloca', '-I/usr/local/include/opus', '-I/usr/local/include', '-I/usr/local/include/dbus-1.0', '-I/usr/local/lib/dbus-1.0/include', '-DEXECINFO=1', '-DHAVE_LIBSYSINFO=1', '-DHAVE_DOXYGEN=0', '-DHAVE_ALSA=0', '-DHAVE_FIREWIRE=0', '-DHAVE_IIO=0', '-DHAVE_PORTAUDIO=0', '-DHAVE_WINMME=0', '-DHAVE_CELT=0', '-DHAVE_EXAMPLE_TOOLS=0', '-DHAVE_OPUS_OPUS_CUSTOM_H=1', '-DHAVE_OPUS_PKG=1', '-DHAVE_OPUS=1', '-DHAVE_SAMPLERATE=1', '-DHAVE_SNDFILE=0', '-DHAVE_READLINE=0', '-DHAVE_SYSTEMD=0', '-DHAVE_DB_H=1', '-DHAVE_DB=0', '-DHAVE_ZALSA=0', '-DHAVE_PPOLL=1', '-DHAVE_EXECINFO_H=1', '-DJACK_VERSION="[]"', '-DHAVE_DBUS_1=1', '-DHAVE_EXPAT=1', '-DUSE_LIBDBUS_AUTOLAUNCH=1', '-DCLIENT_NUM=256', '-DPORT_NUM_FOR_CLIENT=2048', '-DADDON_DIR="/usr/local/lib/jack"', '-DJACK_LOCATION="/usr/local/bin"', '-DUSE_POSIX_SHM=1', '-DJACKMP=1', '-DJACK_DBUS=1', '-DHAVE_CONFIG_H', '-DSERVER_SIDE', '../common/JackDebugClient.cpp', '-c', '-o/wrkdirs/usr/ports/audio/jack/work/jack2-1.9.20/build/common/JackDebugClient.cpp.2.o', '-I/usr/local/include']
In file included from ../common/JackDebugClient.cpp:21:
../common/JackEngineControl.h:67:5: error: requested alignment is less than minimum alignment of 8 for type 'Jack::JackTransportEngine'

alignas(UInt32) JackTransportEngine fTransport;
^

../common/JackEngineControl.h:89:5: error: requested alignment is less than minimum alignment of 8 for type 'Jack::JackFrameTimer'

alignas(UInt32) JackFrameTimer fFrameTimer;
^

2 errors generated.