@cfunction: swap at, rt (#33267)

swap at (types of arguments) and rt (return value type).

base/c.jl

@@ -61,20 +61,20 @@ julia> @cfunction(foo, Int, (Int, Int))
 Ptr{Cvoid} @0x000000001b82fcd0
 ```
 """
-macro cfunction(f, at, rt)
-    if !(isa(rt, Expr) && rt.head === :tuple)
+macro cfunction(f, rt, at)
+    if !(isa(at, Expr) && at.head === :tuple)
         throw(ArgumentError("@cfunction argument types must be a literal tuple"))
     end
-    rt.head = :call
-    pushfirst!(rt.args, GlobalRef(Core, :svec))
+    at.head = :call
+    pushfirst!(at.args, GlobalRef(Core, :svec))
     if isa(f, Expr) && f.head === :$
         fptr = f.args[1]
         typ = CFunction
     else
         fptr = QuoteNode(f)
         typ = Ptr{Cvoid}
     end
-    cfun = Expr(:cfunction, typ, fptr, at, rt, QuoteNode(:ccall))
+    cfun = Expr(:cfunction, typ, fptr, rt, at, QuoteNode(:ccall))
     return esc(cfun)
 end