new tests

[Philip Blundell]

I've checked in a handful of new test cases for gas and ld.  On most platforms 
these shouldn't introduce any new failures.

The new gas test `arm/msr-bad' fails at the moment; I think this is a relatively 
recent piece of breakage, though I haven't investigated yet.

The new ld test `ld-undefined/weak-undef' is only enabled for ELF targets.  
I'm not sure whether COFF targets are supposed to support this or not; i386-pe 
does, but it might be the only one.

BTW, I think ld-elfvsb/elfvsb.exp and ld-shared/shared.exp should probably be 
enabled for Alpha too.  Anybody care to try it out?

p.