[clang][Interp] Ignore unnamed bitfields when zeroing records (#102749)

Including unions, where this is more important.

Author: tbaederr

clang/lib/AST/Interp/Compiler.cpp

@@ -3356,6 +3356,9 @@ bool Compiler<Emitter>::visitZeroRecordInitializer(const Record *R,
   assert(R);
   // Fields
   for (const Record::Field &Field : R->fields()) {
+    if (Field.Decl->isUnnamedBitField())
+      continue;
+
     const Descriptor *D = Field.Desc;
     if (D->isPrimitive()) {
       QualType QT = D->getType();

clang/test/AST/Interp/unions.cpp

@@ -297,5 +297,13 @@ namespace Zeroing {
   static_assert(u6.a[4] == 0, "");
   static_assert(u6.b == 0, ""); // both-error {{not an integral constant expression}} \
                                 // both-note {{read of member 'b' of union with active member 'a'}}
+
+  union UnionWithUnnamedBitfield {
+    int : 3;
+    int n;
+  };
+  static_assert(UnionWithUnnamedBitfield().n == 0, "");
+  static_assert(UnionWithUnnamedBitfield{}.n == 0, "");
+  static_assert(UnionWithUnnamedBitfield{1}.n == 1, "");
 }
 #endif