Fix GTests compilations on Windows

Unfortunately this doesn't make all tests compilable due
to all sort of weird and wonderful bad levels includes
on Windows (G referenced from bf_blenlib) but at least
allows to selectively build tests for now.

build_files/cmake/Modules/GTestTesting.cmake

@@ -29,6 +29,7 @@ macro(BLENDER_SRC_GTEST_EX NAME SRC EXTRA_LIBS DO_ADD_TEST)
 		add_executable(${NAME}_test ${SRC})
 		target_link_libraries(${NAME}_test
 		                      ${EXTRA_LIBS}
+		                      ${PLATFORM_LINKLIBS}
 		                      bf_testing_main
 		                      bf_intern_guardedalloc
 		                      extern_gtest

tests/gtests/testing/CMakeLists.txt

@@ -47,4 +47,7 @@ set(SRC
 	testing.h
 )
 
+add_definitions(${GFLAGS_DEFINES})
+add_definitions(${GLOG_DEFINES})
+
 blender_add_lib(bf_testing_main "${SRC}" "${INC}" "${INC_SYS}")