[clang][bytecode] Use first FieldDecl instead of asserting (llvm#104760)

This assertion fails sometimes. We use the first decl for lookup later,
so let's use the first decl here as well.

Author: tbaederr

clang/lib/AST/ByteCode/Program.cpp

@@ -329,7 +329,7 @@ Record *Program::getOrCreateRecord(const RecordDecl *RD) {
   // Reserve space for fields.
   Record::FieldList Fields;
   for (const FieldDecl *FD : RD->fields()) {
-    assert(FD == FD->getFirstDecl());
+    FD = FD->getFirstDecl();
     // Note that we DO create fields and descriptors
     // for unnamed bitfields here, even though we later ignore
     // them everywhere. That's so the FieldDecl's getFieldIndex() matches.

clang/test/Modules/merge-using-decls.cpp

@@ -6,7 +6,8 @@
 // RUN: %clang_cc1 -fmodules -fimplicit-module-maps -fmodules-cache-path=%t -x c++ -I%S/Inputs/merge-using-decls -verify %s -DORDER=2
 // RUN: %clang_cc1 -fmodules -fimplicit-module-maps -fmodules-cache-path=%t -x c++ -I%S/Inputs/merge-using-decls -verify -std=c++98 %s -DORDER=2
 // RUN: %clang_cc1 -fmodules -fimplicit-module-maps -fmodules-cache-path=%t -x c++ -I%S/Inputs/merge-using-decls -verify -std=c++11 %s -DORDER=2
-// RUN: %clang_cc1 -fmodules -fimplicit-module-maps -fmodules-cache-path=%t -x c++ -I%S/Inputs/merge-using-decls -verify -std=c++17 %s -DORDER=2
+
+// RUN: %clang_cc1 -fexperimental-new-constant-interpreter -fmodules -fimplicit-module-maps -fmodules-cache-path=%t -x c++ -I%S/Inputs/merge-using-decls -verify -std=c++17 %s -DORDER=2
 
 #if ORDER == 1
 #include "a.h"