[cxx-interop] Members of private base classes should not be exposed

Trying to use members of C++ private base classes from Swift causes an assertion failure in ClangImporter:

```
<build dir>/swift/lib/swift/macosx/arm64/libcxxshim.h:2:66: error: cannot cast 'A' to its private base class 'B'
To __swift_interopStaticCast(From from) { return static_cast<To>(from); }
                                                                 ^
```

Such members should not be exposed.

rdar://103871000

Author: egorzhdan

lib/ClangImporter/ClangImporter.cpp

@@ -5007,6 +5007,9 @@ TinyPtrVector<ValueDecl *> ClangRecordMemberLookup::evaluate(
   if (auto cxxRecord =
           dyn_cast<clang::CXXRecordDecl>(recordDecl->getClangDecl())) {
     for (auto base : cxxRecord->bases()) {
+      if (base.getAccessSpecifier() != clang::AccessSpecifier::AS_public)
+        continue;
+
       clang::QualType baseType = base.getType();
       if (auto spectType = dyn_cast<clang::TemplateSpecializationType>(baseType))
         baseType = spectType->desugar();

lib/ClangImporter/ImportDecl.cpp

@@ -8442,6 +8442,9 @@ void ClangImporter::Implementation::loadAllMembersOfRecordDecl(
   // If this is a C++ record, look through the base classes too.
   if (auto cxxRecord = dyn_cast<clang::CXXRecordDecl>(clangRecord)) {
     for (auto base : cxxRecord->bases()) {
+      if (base.getAccessSpecifier() != clang::AccessSpecifier::AS_public)
+        continue;
+
       clang::QualType baseType = base.getType();
       if (auto spectType = dyn_cast<clang::TemplateSpecializationType>(baseType))
         baseType = spectType->desugar();

test/Interop/Cxx/class/inheritance/Inputs/functions.h

@@ -77,6 +77,12 @@ struct DerivedFromDerived : Derived {
 struct __attribute__((swift_attr("import_unsafe"))) DerivedFromNonTrivial
     : NonTrivial {};
 
+struct PrivatelyInherited : private Base {
+};
+
+struct ProtectedInherited : protected Base {
+};
+
 struct EmptyBaseClass {
   const char *inBase() const __attribute__((swift_attr("import_unsafe"))) {
     return "EmptyBaseClass::inBase";

test/Interop/Cxx/class/inheritance/functions-module-interface.swift

@@ -92,3 +92,11 @@
 // CHECK-NEXT:   @discardableResult
 // CHECK-NEXT:   func inNonTrivialWithArgs(_ a: Int32, _ b: Int32) -> UnsafePointer<CChar>?
 // CHECK-NEXT: }
+
+// CHECK-NEXT: struct PrivatelyInherited {
+// CHECK-NEXT:   init()
+// CHECK-NEXT: }
+
+// CHECK-NEXT: struct ProtectedInherited {
+// CHECK-NEXT:   init()
+// CHECK-NEXT: }

test/Interop/Cxx/class/inheritance/extensions-typechecker.swift renamed to test/Interop/Cxx/class/inheritance/functions-typechecker.swift

@@ -2,6 +2,10 @@
 
 import Functions
 
+PrivatelyInherited().constInBase() // expected-error {{value of type 'PrivatelyInherited' has no member 'constInBase'}}
+ProtectedInherited().constInBase() // expected-error {{value of type 'ProtectedInherited' has no member 'constInBase'}}
+
+
 extension Base {
   public func swiftFunc() {}
 }