[Verifier] Allow DW_TAG_class_type/DW_TAG_union_type to have no filename

`clang/lib/CodeGen/CGOpenMPRuntime.cpp` synthesized union
(`distinct !DICompositeType(tag: DW_TAG_union_type, name: "kmp_cmplrdata_t", size: 64, elements: <0x62b690>)`)
does not have meaningful filename/line number.

D94735 dropped the previously arbitrary and untested filename/line from the union and caused a verifier error here.

This fixes `check-libarcher` failures.

Differential Revision: https://reviews.llvm.org/D96212

llvm/lib/IR/Verifier.cpp

@@ -1070,12 +1070,6 @@ void Verifier::visitDICompositeType(const DICompositeType &N) {
   if (auto *Params = N.getRawTemplateParams())
     visitTemplateParams(N, *Params);
 
-  if (N.getTag() == dwarf::DW_TAG_class_type ||
-      N.getTag() == dwarf::DW_TAG_union_type) {
-    AssertDI(N.getFile() && !N.getFile()->getFilename().empty(),
-             "class/union requires a filename", &N, N.getFile());
-  }
-
   if (auto *D = N.getRawDiscriminator()) {
     AssertDI(isa<DIDerivedType>(D) && N.getTag() == dwarf::DW_TAG_variant_part,
              "discriminator can only appear on variant part");