Introduce AbstractFunctionDecl -- a base class for ConstructorDecl,

DestructorDecl, FuncDecl -- and move some of the common concepts and logic
into it

No functionality change.


Swift SVN r8090

lib/Serialization/ModuleFormat.h

@@ -567,6 +567,7 @@ namespace decls_block {
     BCFixed<1>,   // explicitly objc?
     BCFixed<1>,   // iboutlet?
     BCFixed<1>,   // transparent?
+    BCVBR<5>,     // number of parameter patterns
     TypeIDField,  // type (signature)
     DeclIDField,  // operator decl
     DeclIDField,  // overridden function