Myself and others new to mbed having trouble understanding the various arcane requirements. Adding a mbed_app.json file to enable a library feature instead of using a #define is one of them. Sharing this to help others.

Dependencies:   max32630fthr USBDevice

Revision:
9:29f7bb957c34
Parent:
8:d2b660bf5f94
--- a/mbed-os.lib	Thu Nov 16 21:27:19 2017 +0000
+++ b/mbed-os.lib	Fri Apr 05 01:44:50 2019 +0000
@@ -1,1 +1,1 @@
-https://github.com/ARMmbed/mbed-os/#78474a5129e18e136cc7e872adbaa5b74fbb8f6a
+https://github.com/ARMmbed/mbed-os/#51d55508e8400b60af467005646c4e2164738d48