Driver: ArgList::getLastArg was in fact returning the first matching arg.
 - <rdar://problem/6715818> clang doesn't honor gcc semantic that last
    -O optimization option wins.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@67628 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Driver/ArgList.cpp b/lib/Driver/ArgList.cpp
index 7653daf..d74e3bd 100644
--- a/lib/Driver/ArgList.cpp
+++ b/lib/Driver/ArgList.cpp
@@ -34,9 +34,7 @@
 
 Arg *ArgList::getLastArg(options::ID Id, bool Claim) const {
   // FIXME: Make search efficient?
-
-  // FIXME: This needs to not require loading of the option.
-  for (const_iterator it = begin(), ie = end(); it != ie; ++it) {
+  for (const_reverse_iterator it = rbegin(), ie = rend(); it != ie; ++it) {
     if ((*it)->getOption().matches(Id)) {
       if (Claim) (*it)->claim();
       return *it;