[Clang] prevent assertion on empty filename in #embed directive (llvm#163072)

Fixes llvm#162951

---

This PR addresses the issue of Clang asserting when processing `#embed`
with an empty filename

```c
#embed <>
```

Author: a-tarasyuk

clang/docs/ReleaseNotes.rst

@@ -408,6 +408,7 @@ Bug Fixes in This Version
   a function without arguments caused us to try to access a non-existent argument.
   (#GH159080)
 - Fixed a failed assertion with empty filename arguments in ``__has_embed``. (#GH159898)
+- Fixed a failed assertion with empty filename in ``#embed`` directive. (#GH162951)
 
 Bug Fixes to Compiler Builtins
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

clang/lib/Lex/PPDirectives.cpp

@@ -3991,9 +3991,12 @@ void Preprocessor::HandleEmbedDirective(SourceLocation HashLoc, Token &EmbedTok,
   StringRef OriginalFilename = Filename;
   bool isAngled =
       GetIncludeFilenameSpelling(FilenameTok.getLocation(), Filename);
+
   // If GetIncludeFilenameSpelling set the start ptr to null, there was an
   // error.
-  assert(!Filename.empty());
+  if (Filename.empty())
+    return;
+
   OptionalFileEntryRef MaybeFileRef =
       this->LookupEmbedFile(Filename, isAngled, true, LookupFromFile);
   if (!MaybeFileRef) {

clang/test/Preprocessor/embed_empty_file.c

@@ -0,0 +1,4 @@
+// RUN: %clang_cc1 -std=c23 %s -E -verify
+
+#embed <> // expected-error {{empty filename}}
+#embed "" // expected-error {{empty filename}}