Versioning longjmp etc.

[Steve Munroe]

Ulrich Drepper writes:

> Why should this be necessary?  It makes almost no sense at all to
> include the content of these registers in the state. setjmp/longjmp are
> probably never used in the middle of computations in which vector
> registers are used.

For the future when gcc supports autovectorization.

I want to make VMX as usable as possible, without undefined behaviors or 
undocumented restrictions. 

How about get/set/make/swapcontext? The size of ucontext will change as a 
result of VMX state in sigcontext. This requires versioning.