Enable ASSERTS's in nrf sdk to catch coding errors.

These will now flow through to mbed standard error handling.

features/FEATURE_BLE/targets/TARGET_NORDIC/TARGET_NRF51/source/btle/btle.cpp

@@ -299,10 +299,10 @@ static void btle_handler(ble_evt_t *p_ble_evt)
     gattServer.hwCallback(p_ble_evt);
 }
 
-/*! @brief      Callback when an error occurs inside the SoftDevice */
+/*! @brief      Callback when an error occurs inside the SoftDevice or ASSERT in debug*/
 void assert_nrf_callback(uint16_t line_num, const uint8_t *p_file_name)
 {
-    ASSERT_TRUE(false, (void) 0);
+    error("nrf failure at %s:%d", p_file_name, line_num);
 }
 
 /*!

targets/targets.json

@@ -3450,7 +3450,8 @@
             "CMSIS_VECTAB_VIRTUAL",
             "CMSIS_VECTAB_VIRTUAL_HEADER_FILE=\"cmsis_nvic.h\"",
             "NO_SYSTICK",
-            "MBED_TICKLESS"
+            "MBED_TICKLESS",
+            "DEBUG_NRF_USER"
         ],
         "MERGE_BOOTLOADER": false,
         "extra_labels": [