[clang-tidy] give dummy path when create ClangTidyContext (llvm#134670)

llvm#121323 changed the way the absolute path is computed. Empty file name
will cause absolute path ignore current folder.
This patch add "dummy" file name to avoid this issue
Fixed: llvm#134502

Author: HerrCai0907

clang-tools-extra/clang-tidy/ClangTidyDiagnosticConsumer.cpp

@@ -167,8 +167,8 @@ ClangTidyContext::ClangTidyContext(
       AllowEnablingAnalyzerAlphaCheckers(AllowEnablingAnalyzerAlphaCheckers),
       EnableModuleHeadersParsing(EnableModuleHeadersParsing) {
   // Before the first translation unit we can get errors related to command-line
-  // parsing, use empty string for the file name in this case.
-  setCurrentFile("");
+  // parsing, use dummy string for the file name in this case.
+  setCurrentFile("dummy");
 }
 
 ClangTidyContext::~ClangTidyContext() = default;