[ASTImporter] Implement some expression-related AST node import (part 2)

* Some code cleanup
* Add tests not present in http://reviews.llvm.org/D14286
* Integrate a test suite from Serge Pavlov (http://reviews.llvm.org/D14224)
* ArrayTypeTraitExpr: serialize sub-expression to avoid keeping it undefined
* Implement import of some nodes:
  - ArrayTypeTraitExpr
  - ExpressionTraitExpr
  - OpaqueValueExpr
  - ArraySubscriptExpr
  - ExplicitCastExpr
  - ImplicitValueInitExpr
  - OffsetOfExpr
  - CXXThisExpr
  - CXXThrowExpr
  - CXXNoexceptExpr
  - CXXDefaultArgExpr
  - CXXScalarValueInitExpr
  - CXXBindTemporaryExpr
  - CXXTemporaryObjectExpr
  - MaterializeTemporaryExpr
  - ExprWithCleanups

  - StaticAssertDecl
  - FriendDecl

  - DecayedType

Differential Revision: https://reviews.llvm.org/D14326

llvm-svn: 282572
diff --git a/clang/test/ASTMerge/exprs.cpp b/clang/test/ASTMerge/exprs.cpp
new file mode 100644
index 0000000..ba1f18b
--- /dev/null
+++ b/clang/test/ASTMerge/exprs.cpp
@@ -0,0 +1,45 @@
+// RUN: %clang_cc1 -triple %itanium_abi_triple -std=c++1z -fcxx-exceptions -emit-pch -o %t.1.ast %S/Inputs/exprs3.cpp
+// RUN: %clang_cc1 -triple %itanium_abi_triple -std=c++1z -fcxx-exceptions -ast-merge %t.1.ast -fsyntax-only -verify %s
+// expected-no-diagnostics
+
+static_assert(Ch1 == 'a');
+static_assert(Ch2 == 'b');
+static_assert(Ch3 == 'c');
+
+static_assert(Ch4 == L'd');
+static_assert(Ch5 == L'e');
+static_assert(Ch6 == L'f');
+
+static_assert(C1 == 12);
+static_assert(C2 == 13);
+
+static_assert(C3 == 12);
+static_assert(C4 == 13);
+
+static_assert(C5 == 22L);
+static_assert(C6 == 23L);
+
+static_assert(C7 == 66LL);
+static_assert(C8 == 67ULL);
+
+static_assert(bval1 == true);
+static_assert(bval2 == false);
+
+static_assert(ExpressionTrait == false);
+
+static_assert(ArrayRank == 2);
+static_assert(ArrayExtent == 20);
+
+void testImport(int *x, const S1 &cs1, S1 &s1) {
+  testNewThrowDelete();
+  testArrayElement(nullptr, 12);
+  testTernaryOp(0, 1, 2);
+  testConstCast(cs1);
+  testStaticCast(s1);
+  testReinterpretCast(s1);
+  testDynamicCast(s1);
+  testScalarInit(42);
+  testOffsetOf();
+  testDefaultArg(12);
+  useTemplateType();
+}