swift234

AST: Add Throws flag and ThrowsLoc to AbstractFunctionDecl

The verifier now asserts that Throws, ThrowsLoc and isBodyThrowing()
match up.

Also, add /*Label=*/ comments where necessary to make the long argument
lists easier to read, and cleaned up some inconsistent naming conventions.

I caught a case where ClangImporter where we were passing in a loc as
StaticLoc instead of FuncLoc, but probably this didn't affect anything.