Upgrade gflags to master

Merge commit 'cb7bb2b58469b0ba5132fbcf4893b2ca76dead1c' into master

Change-Id: Id6b07c15b3bef794984d6f326d6596f043d1dde5
diff --git a/build_tests/gflags.cc b/build_tests/gflags.cc
index 150e330..20ce987 100644
--- a/build_tests/gflags.cc
+++ b/build_tests/gflags.cc
@@ -1,4 +1,4 @@
-#include "third_party/gflags/include/gflags/gflags.h"
+#include "gflags/gflags.h"
 
 DEFINE_int32(test_flag, 0, "Test command-line flag");