ASTDemangler: Make it work from lldb

For some reason, findDeclContext() finds the special ClangImporter
module from inside lldb, and then we were skipping the logic in
findForeignTypeDecl(). So check for the foreign type case first.

Author: slavapestov

lib/AST/ASTDemangler.cpp

@@ -802,16 +802,17 @@ ASTBuilder::findDeclContext(const Demangle::NodePointer &node) {
       return nullptr;
     }
 
+    // Do some special logic for foreign type declarations.
+    if (privateDiscriminator.empty()) {
+      if (auto foreignModuleKind = getForeignModuleKind(node->getChild(0))) {
+        return findForeignTypeDecl(name, relatedEntityKind,
+                                    foreignModuleKind.getValue(),
+                                    node->getKind());
+      }
+    }
+
     DeclContext *dc = findDeclContext(node->getChild(0));
     if (!dc) {
-      // Do some backup logic for foreign type declarations.
-      if (privateDiscriminator.empty()) {
-        if (auto foreignModuleKind = getForeignModuleKind(node->getChild(0))) {
-          return findForeignTypeDecl(name, relatedEntityKind,
-                                     foreignModuleKind.getValue(),
-                                     node->getKind());
-        }
-      }
       return nullptr;
     }