Adding target specific tests

[Elena Zannoni]

I am about to add 2 new testfiles to the gdb testsuite. Both are
specific to Altivec. One is a generic test for the ABI (function calls
and return values), the other deals with the AltiVec registers.

Where should I put them?
I was thinking of adding a gdb.altivec directory to gdb/testsuite.
Or a gdb.powerpc?
Or a gdb.regs and a gdb.abi?

I really don't know what the best solution would be. These tests
certainly cannot go in gdb.base.

Ideas? Opinions?

Elena