To load unaligned vector data in the usual way, explicit vec_ld()
should be used rather than dereferencing a pointer to a vector type.
When the VSX extension is enabled, gcc may compile vector pointer
dereferences using the VSX lxvw4x instruction instead of the lvx
instruction typically used with Altivec/VMX.  As the behaviour of
these instructions with unaligned addresses differs, it is important
that only lvx is used here.
Signed-off-by: Mans Rullgard <mans@mansr.com>