[DebugLine] Be more robust in geussing the path style

My previous change didn't fix the Windows bot. This patch is an attempt
to make guessing the path style more robust by first looking at the
compile dir and falling back to the actual file if that's unsuccessful.

llvm-svn: 368772

Author: JDevlieghere

lldb/source/Plugins/SymbolFile/DWARF/SymbolFileDWARF.cpp

@@ -186,6 +186,8 @@ ParseSupportFilesFromPrologue(const lldb::ModuleSP &module,
   FileSpecList support_files;
   support_files.Append(first_file);
 
+  llvm::Optional<FileSpec::Style> compile_dir_style =
+      FileSpec::GuessPathStyle(compile_dir);
   const size_t number_of_files = prologue.FileNames.size();
   for (size_t idx = 1; idx <= number_of_files; ++idx) {
     std::string original_file;
@@ -198,9 +200,13 @@ ParseSupportFilesFromPrologue(const lldb::ModuleSP &module,
       continue;
     }
 
-    auto maybe_path_style = FileSpec::GuessPathStyle(original_file);
-    FileSpec::Style style =
-        maybe_path_style ? *maybe_path_style : FileSpec::Style::native;
+    FileSpec::Style style = FileSpec::Style::native;
+    if (compile_dir_style) {
+      style = *compile_dir_style;
+    } else if (llvm::Optional<FileSpec::Style> file_style =
+                   FileSpec::GuessPathStyle(original_file)) {
+      style = *file_style;
+    }
 
     std::string remapped_file;
     if (!prologue.getFileNameByIndex(