altivec backend broken on ppc64le

I came across this after the most recent release was merged in my distro, when something calls into orc with the altivec support enabled, it crashes with something like this:

Thread 65 "task3" received signal SIGILL, Illegal instruction.
[Switching to Thread 0x7ffeab7ef070 (LWP 80434)]
0x00007fff54560004 in ?? ()
(gdb) bt
#0  0x00007fff54560004 in  ()
#1  0x00007fff9001583c in orc_memset (d1=0x7ffe9c037800, p1=<optimized out>, n=<optimized out>) at ../orc/orcfunctions.c:321
#2  0x00007fff901b4270 in gst_audio_format_fill_silence () at /usr/lib/libgstaudio-1.0.so.0
#3  0x00007fff901cd2c8 in gst_audio_ring_buffer_acquire () at /usr/lib/libgstaudio-1.0.so.0

This is on POWER8 little endian.