[ASTImporter] Implement missing VisitAccessSpecDecl function in ASTImporter class.

Patch by Elisavet Sakellari!

llvm-svn: 261274
diff --git a/clang/test/ASTMerge/Inputs/class1.cpp b/clang/test/ASTMerge/Inputs/class1.cpp
index 0cd6565..b0a7645 100644
--- a/clang/test/ASTMerge/Inputs/class1.cpp
+++ b/clang/test/ASTMerge/Inputs/class1.cpp
@@ -1,5 +1,6 @@
 struct A {
-  int x;
+  public:
+    int x;
 };
 
 struct B : A {