Fixes for compiling with -fno-common, default in GCC 10.

Taken from upstream:
https://github.com/qca/open-ath9k-htc-firmware/commit/559e3eba3b4cf103da6b8d022f3e1387278b9db8

diff --git a/target_firmware/magpie_fw_dev/target/init/app_start.c b/target_firmware/magpie_fw_dev/target/init/app_start.c
--- a/target_firmware/magpie_fw_dev/target/init/app_start.c
+++ b/target_firmware/magpie_fw_dev/target/init/app_start.c
@@ -52,6 +52,8 @@
 #define ALLOCRAM_START       ( ((unsigned int)&_fw_image_end) + 4)
 #define ALLOCRAM_SIZE        ( SYS_RAM_SZIE - ( ALLOCRAM_START - SYS_D_RAM_REGION_0_BASE) - SYS_D_RAM_STACK_SIZE)
 
+void (* _assfail_ori)(struct register_dump_s *);
+
 // support for more than 64 bytes on command pipe
 extern void usb_reg_out_patch(void);
 extern int _HIFusb_get_max_msg_len_patch(hif_handle_t handle, int pipe);
diff --git a/target_firmware/magpie_fw_dev/target/init/init.h b/target_firmware/magpie_fw_dev/target/init/init.h
--- a/target_firmware/magpie_fw_dev/target/init/init.h
+++ b/target_firmware/magpie_fw_dev/target/init/init.h
@@ -46,7 +46,7 @@
 void AR6002_fatal_exception_handler_patch(CPU_exception_frame_t *exc_frame);
 void exception_reset(struct register_dump_s *dump);
 
-void (* _assfail_ori)(struct register_dump_s *);
+extern void (* _assfail_ori)(struct register_dump_s *);
 void HTCMsgRecvHandler_patch(adf_nbuf_t hdr_buf, adf_nbuf_t buffer, void *context);
 void HTCControlSvcProcessMsg_patch(HTC_ENDPOINT_ID EndpointID, adf_nbuf_t hdr_buf,
 				   adf_nbuf_t pBuffers, void *arg);