Cope with anonymous tags defined within declarators by structurally
comparing their types under the assumption that they are equivalent,
rather than importing the types and then checking for compatibility. A
few minor tweaks here:
  - Teach structural matching to handle compatibility between
  function types with prototypes and those without prototypes.
  - Teach structural matching that an incomplete record decl is the
  same as any other record decl with the same name.
  - Keep track of pairs of declarations that we have already checked
  (but failed to find as structurally matching), so we don't emit
  diagnostics repeatedly.
  - When importing a typedef of an anonymous tag, be sure to link the
  imported tag type to its typedef.

With these changes, we survive a repeated import of <stdlib.h> and
<stdio.h>. Alas, the ASTNodeImporter is getting a little grotty.



git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@96298 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/test/ASTMerge/Inputs/function2.c b/test/ASTMerge/Inputs/function2.c
index ad81c07..6ca810a 100644
--- a/test/ASTMerge/Inputs/function2.c
+++ b/test/ASTMerge/Inputs/function2.c
@@ -4,3 +4,4 @@
 void f2(int, int);
 void f3(int);
 static void f4(float, float);
+int f5(int) __attribute__((const));