[HIPIFY] Introduce '--' option - a separator between hipify-clang and clang options

+ Append '--' to the end of hipify-clang options in case of its absence.

[Reason]
+ Avoid the necessity for the user in JSON compilation database specification.
  Otherwise:
  Error while trying to load a compilation database:
  Could not auto-detect compilation database for file "test.cu"

  Though the hipification will be performed correctly without JSON database.

hipify-clang/src/ArgParse.cpp

@@ -84,4 +84,9 @@ cl::opt<bool> Examine("examine",
   cl::value_desc("examine"),
   cl::cat(ToolTemplateCategory));
 
+cl::opt<bool> DashDash("-",
+  cl::desc("Separator between hipify-clang and clang options;\ndon't specify if there are no clang options."),
+  cl::value_desc("--"),
+  cl::cat(ToolTemplateCategory));
+
 cl::extrahelp CommonHelp(ct::CommonOptionsParser::HelpMessage);