Output: Skip implicit members that cannot be compiled

Implement the HandleTagDeclDefinition method in our ASTConsumer.  Clang
calls this method during parsing on completion of each class definition.
This gives us a chance to modify class definitions.

Teach HandleTagDeclDefinition to add the implicit member declarations.
For each implicit member, ask Clang to try instantiating its definition
to see if a call to the member will actually work.  Suppress errors
during this check using a clang::Sema::SFINAETrap and simply mark
the declaration as invalid if there were errors.

Add test cases for:

* implicit members that cannot be used due to access, const data members,
  or reference data members.

* a POD array data member since Clang uses special logic when creating
  implicit members that copy the data.

* a mutable data member since Clang adds implicit member declarations
  itself (via clang::Sema::AddImplicitlyDeclaredMembersToClass),
  but we still need to try defining them.

* a class that uses its implicit members so they are already defined.

1 files changed, 5 insertions, 0 deletions

diff --git a/test/input/Class-implicit-member-reference.cxx b/test/input/Class-implicit-member-reference.cxx
new file mode 100644
index 0000000..67da21d
--- /dev/null
+++ b/test/input/Class-implicit-member-reference.cxx
@@ -0,0 +1,5 @@
+class start {
+  int& ref;
+public:
+  start();
+};