clang: use auto qualifier in place of const_iterator

Fix build issue with clang 12.0.5:

../../third_party/googletest/googlemock/include/gmock/gmock-matchers.h:3147:33: error: no type named 'const_iterator' in 'std::span<unsigned long, 18446744073709551615>'

Change-Id: If9cb005fca669760bcff6cdafcabec7ffc3abd99
Signed-off-by: Olivier Deprez <olivier.deprez@arm.com>
diff --git a/googlemock/include/gmock/gmock-matchers.h b/googlemock/include/gmock/gmock-matchers.h
index a7bcfc8..5af330e 100644
--- a/googlemock/include/gmock/gmock-matchers.h
+++ b/googlemock/include/gmock/gmock-matchers.h
@@ -3144,7 +3144,7 @@
                            MatchResultListener* listener) const {
     StlContainerReference stl_container = View::ConstReference(container);
     size_t i = 0;
-    for (typename StlContainer::const_iterator it = stl_container.begin();
+    for (auto it = stl_container.begin();
          it != stl_container.end(); ++it, ++i) {
       StringMatchResultListener inner_listener;
       const bool matches = inner_matcher_.MatchAndExplain(*it, &inner_listener);
@@ -3538,7 +3538,7 @@
     // explanations[i] is the explanation of the element at index i.
     ::std::vector<std::string> explanations(count());
     StlContainerReference stl_container = View::ConstReference(container);
-    typename StlContainer::const_iterator it = stl_container.begin();
+    auto it = stl_container.begin();
     size_t exam_pos = 0;
     bool mismatch_found = false;  // Have we found a mismatched element yet?