added clock_source for tests

Author: Roberto Spelta

targets/targets.json

@@ -1372,6 +1372,13 @@
         "core": "Cortex-M4F",
         "default_toolchain": "GCC_ARM",
         "extra_labels_add": ["STM32L4", "STM32L476xG", "STM32L476JG"],
+        "config": {
+            "clock_source": {
+                "help": "Mask value : USE_PLL_HSE_EXTC (need HW patch) | USE_PLL_HSE_XTAL (need HW patch) | USE_PLL_HSI | USE_PLL_MSI",
+                "value": "USE_PLL_MSI",
+                "macro_name": "CLOCK_SOURCE"
+            }
+        },
         "detect_code": ["0766"],
         "macros_add": ["USBHOST_OTHER"],
         "device_has_add": ["ANALOGOUT", "CAN", "LOWPOWERTIMER", "SERIAL_ASYNCH", "SERIAL_FC", "TRNG", "FLASH"],