THRIFT-4165: better cmake support for C++ language level selection; fixed compiler warnings

This closes #1236
diff --git a/build/cmake/DefineOptions.cmake b/build/cmake/DefineOptions.cmake
index 93fe2c0..63981e9 100644
--- a/build/cmake/DefineOptions.cmake
+++ b/build/cmake/DefineOptions.cmake
@@ -173,6 +173,7 @@
 message(STATUS "  Build C++ library:                          ${BUILD_CPP}")
 MESSAGE_DEP(WITH_CPP "Disabled by WITH_CPP=OFF")
 MESSAGE_DEP(Boost_FOUND "Boost headers missing")
+message(STATUS "    C++ Language Level:                       ${CXX_LANGUAGE_LEVEL}")
 message(STATUS "  Build C (GLib) library:                     ${BUILD_C_GLIB}")
 MESSAGE_DEP(WITH_C_GLIB "Disabled by WITH_C_GLIB=OFF")
 MESSAGE_DEP(GLIB_FOUND "GLib missing")