Give a warning when no dwo files are provided (#94336)

In some scenarios based on the split-dwarf build process, the dwo file
is not generated as expected(That is to say, no dwo file path is stored
in the binary). When the llvm-dwp tool is called to generate the .dwp
file, it will exit without any warning.
 
So, the plan is to prompt a warning to tell the user that the dwo file
was not actually generated.
<img width="699" alt="image"
src="https://github.com/llvm/llvm-project/assets/150100070/5e5742f6-daad-450f-87e9-cb25449c3c7a">

1 files changed, 4 insertions, 1 deletions

diff --git a/llvm/tools/llvm-dwp/llvm-dwp.cpp b/llvm/tools/llvm-dwp/llvm-dwp.cpp
index 4c4f2a9..18f4f1a 100644
--- a/llvm/tools/llvm-dwp/llvm-dwp.cpp
+++ b/llvm/tools/llvm-dwp/llvm-dwp.cpp
@@ -188,8 +188,11 @@ int llvm_dwp_main(int argc, char **argv, const llvm::ToolContext &) {
                         std::make_move_iterator(DWOs->end()));
   }
 
-  if (DWOFilenames.empty())
+  if (DWOFilenames.empty()) {
+    WithColor::defaultWarningHandler(make_error<DWPError>(
+        "executable file does not contain any references to dwo files"));
     return 0;
+  }
 
   std::string ErrorStr;
   StringRef Context = "dwarf streamer init";