Fix gtest build in cmake.

Change-Id: Ic6a99b82e92f8512bdd40d002aa6b904b768ae9a
diff --git a/CMakeLists.txt b/CMakeLists.txt
index 7bec9a4..5089e41 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -860,7 +860,8 @@
 endif ()
 
 if (CONFIG_UNIT_TESTS)
-  include_directories("${AOM_ROOT}/third_party/googletest/src/include")
+  include_directories("${AOM_ROOT}/third_party/googletest/src/include"
+                      "${AOM_ROOT}/third_party/googletest/src")
 
   add_library(aom_gtest OBJECT ${AOM_GTEST_SOURCES})