swift234

1) Redesign DeclAttributes to be based around an array indexed by attribute, instead
   of having a ton of ad-hoc bools in it.  This allows us to consolidate a ton of 
   boilerplate, eliminating 250 lines of code:

 17 files changed, 435 insertions(+), 662 deletions(-)

2) This eliminates the special case for weak and unowned attributes, which previously
   didn't show up in Attr.def.

3) While we're at it, keep track of proper source locations for each attribute, and
   use these to emit diagnostics pointing at the attribute in question instead of at
   a funcdecl or the @ sign.

4) Fix axle attributes, which had vertex and fragment swapped.



Swift SVN r9263