Driver: Implement 'missing argument' error.

llvm-svn: 67490
diff --git a/clang/lib/Driver/ArgList.cpp b/clang/lib/Driver/ArgList.cpp
index 30da136..7653daf 100644
--- a/clang/lib/Driver/ArgList.cpp
+++ b/clang/lib/Driver/ArgList.cpp
@@ -13,7 +13,9 @@
 
 using namespace clang::driver;
 
-ArgList::ArgList(const char **ArgBegin, const char **ArgEnd) {
+ArgList::ArgList(const char **ArgBegin, const char **ArgEnd) 
+  : NumInputArgStrings(ArgEnd - ArgBegin) 
+{
   ArgStrings.append(ArgBegin, ArgEnd);
 }