fix build after #242

[goloveychuk]

after #242 master is not compilling

[aciidgh]

I don't think this is desired, master should be compiling wrt swift master and not necessarily the toolchain. #242 was done due to proposal SE-0046 which is merged to swift master but isn't in toolchain yet. However I do think #242 should have been CI'ed.

[goloveychuk]

So you saying that

func f(_ arg: Int)
f(arg: 2)

will build in swift/master?
My pr mostly fix this mistakes

[mxcl]

I can build swiftpm master against swift master without this patch.

[goloveychuk]

@mxcl ok, if not needed - can close it. New toolchain will be with master swift. So it wouldn't a problem