[TESTCASE] Minimized testcase for AltiVec segfault

[Kumar Gala]

> how about vrsave?  surely you need vrsave to be set properly, otherwise
> the OS will not save your vector registers on a context-switch.

Does -mabi=altivec cause VRSAVE to be updated?.  On Linux, VRSAVE is not
used by the OS to determine which registers to save (all vr regs are saved
on a context switch).

VRSAVE is useful for ABIs which allocate registers in order (ie MacOS)
such that one can mark the last used register and save/restore to that
point.  Otherwise it seems rather painful to manage/update vrsave in one's
code (for SVR4 style register allocation).

If GCC is managing VRSAVE when -mabi=altivec then I think there should be
another flag to disable the use of VRSAVE.  It tends to be a waste of time
to manage as well as hard to use for determining which regs to save by the
context code.


- kumar