swift234

[Parse] Add fix-its for empty Swift 2 operator decl braces. (#4309)

And improve the error message for non-empty braces; if we're going to
ignore the contents, we should at least point you in the right
direction for Swift 3.

rdar://problem/27576922
(cherry picked from commit 3d005f3ad90f041325e7a28fd9d0544324ac24d6)