Fix CMakeLists.txt for ostringstream_test
Fix CMakeLists.txt for ostringstream_test

After commit 99b92c87 compiling with CMake stopped working. This commit fixes the issue.


firebase/abseil-cpp,abseil/abseil-cpp,abseil/abseil-cpp,firebase/abseil-cpp,abseil/abseil-cpp,firebase/abseil-cpp,abseil/abseil-cpp,firebase/abseil-cpp