Using chrono::steady_clock with ARM Cortex-M4

In trying to use chrono::steady_clock with our Cortex-M4 chip (using ARM's arm-none-eabi-g++ v4.9.3), it seems _GLIBCXX_USE_CLOCK_MONOTONIC is NOT defined in the corresponding "c++config.h" file. This results in the steady_clock::now NOT calling clock_gettime.

How can I get chrono to properly call clock_gettime when using steady_clock::now? Can I simply modify "c++config.h" and recompile? Can I simply define _GLIBCXX_USE_CLOCK_MONOTONIC in an application source file and recompile?