[DebugInfo]Generate call-site information in swift

This patch adds support for emitting the flag
llvm::DINode::FlagAllCallsDescribed when generating LLVM IR from the
Swift compiler to get call-site information for swift source code.

lib/Frontend/CompilerInvocation.cpp

@@ -3681,6 +3681,8 @@ static bool ParseIRGenArgs(IRGenOptions &Opts, ArgList &Args,
   Opts.UseCASBackend |= Args.hasArg(OPT_cas_backend);
   Opts.EmitCASIDFile |= Args.hasArg(OPT_cas_emit_casid_file);
 
+  Opts.DebugCallsiteInfo |= Args.hasArg(OPT_debug_callsite_info);
+
   return false;
 }