[Import as member] forbid swift_name on non-prototyped declarations

Author: milseman

proposals/0044-import-as-member.md

@@ -182,7 +182,7 @@ extern struct Point3D identityPoint
 __attribute__((swift_name("Point3D.identity")));
 
 // Import as static computed property
-Point3D getZeroPoint()
+Point3D getZeroPoint(void)
 __attribute__((swift_name("getter:Point3D.zero()")));
 void setZeroPoint(Point3D point)
 __attribute__((swift_name("setter:Point3D.zero(_:)")));
@@ -195,6 +195,8 @@ The string present in swift_name will additionally support the following:
    method/property, otherwise this will be a static method/property
 * ``getter:`` and ``setter:`` to denote the function as a property getter/setter
 
+*Amendment:* swift_name is not valid on non-prototyped function declarations.
+
 ### Automatic inference heuristics
 
 The following are some techniques and heuristics that can be useful for