Update CMake build to support gflags and gtest correctly

CMakeLists.txt

 cmake_minimum_required(VERSION 2.8)
 
 # CMakeLists for libyuv
 # Originally created for "roxlu build system" to compile libyuv on windows
 # Run with -DTEST=ON to build unit tests
 option(TEST "Built unit tests" OFF)
 
 set(ly_base_dir ${CMAKE_CURRENT_LIST_DIR})
 set(ly_src_dir ${ly_base_dir}/source/)
 set(ly_inc_dir ${ly_base_dir}/include)
@@ skipping 92 matching lines @@
 include(FindJPEG)
 if (JPEG_FOUND)
   include_directories(${JPEG_INCLUDE_DIR})
   target_link_libraries(convert ${JPEG_LIBRARY})
   add_definitions(-DHAVE_JPEG)
 endif()
 
 if(TEST)
   find_library(GTEST_LIBRARY gtest)
   if(GTEST_LIBRARY STREQUAL "GTEST_LIBRARY-NOTFOUND")
-    set(GTEST_SRC_DIR /usr/src/gtest)
+    set(GTEST_SRC_DIR /usr/src/gtest CACHE STRING "Location of gtest sources")
     if(EXISTS ${GTEST_SRC_DIR}/src/gtest-all.cc)
       message(STATUS "building gtest from sources in ${GTEST_SRC_DIR}")
       set(gtest_sources ${GTEST_SRC_DIR}/src/gtest-all.cc)
       add_library(gtest STATIC ${gtest_sources})
       include_directories(${GTEST_SRC_DIR})
+      include_directories(${GTEST_SRC_DIR}/include)
       set(GTEST_LIBRARY gtest)
     else()
       message(FATAL_ERROR "TEST is set but unable to find gtest library")
     endif()
   endif()
 
   add_executable(libyuv_unittest ${ly_unittest_sources})
   target_link_libraries(libyuv_unittest ${ly_lib_name} ${GTEST_LIBRARY} pthread)
   if (JPEG_FOUND)
     target_link_libraries(libyuv_unittest ${JPEG_LIBRARY})
   endif()
 endif()
 
 if(NACL AND NACL_LIBC STREQUAL "newlib")
   target_link_libraries(libyuv_unittest glibc-compat)
 endif()
 
+target_link_libraries(libyuv_unittest gflags)
+
 install(TARGETS ${ly_lib_name} DESTINATION lib)
 install(FILES ${ly_header_files} DESTINATION include/libyuv)
 install(FILES ${ly_inc_dir}/libyuv.h DESTINATION include/)