testsuite/gdb.arch/altivec-abi.exp and testsuite/gdb.arch/altivec-regs.exp 
test for relivance by checking if the configuration string ends in 'altivec'.  
This wasn't working for me and doesn't seem like the right way to do this.

So I replaced it by adding a new routine to testsuit/lib/gdb.exp that compiles 
and runs a tiny little program.  If we are on any machine that doesn't have 
altivec hardware, then either the compile fails or the tiny little program 
gets an illegal instruction trap when run. This is a modification of a 
similar routine in the gcc testsuite. (cut-and-paste code re-use)

I then changed the two tests mentioned above to use the new routine.

Ok to commit?

-=# Paul Gilliam #=-