New experimental/undocumented feature: 'works_on_empty'.

For now, just enough support to make -filelist work.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@96918 91177308-0d34-0410-b5e6-96231b3b80d8

lib/CompilerDriver/Main.cpp

@@ -126,10 +126,6 @@ int Main(int argc, char** argv) {
       return 0;
     }
 
-    if (InputFilenames.empty()) {
-      throw std::runtime_error("no input files");
-    }
-
     if (Time) {
       GlobalTimeLog = new std::stringstream;
       GlobalTimeLog->precision(2);