kernel: backport GCC 10 usbip build fix for 5.4

From the original commit message:

"With GCC 10, building usbip triggers error for multiple definition
of 'udev_context', in:
- libsrc/vhci_driver.c:18 and
- libsrc/usbip_host_common.c:27.

Declare as extern the definition in libsrc/usbip_host_common.c."

Signed-off-by: Rui Salvaterra <rsalvaterra@gmail.com>

target/linux/generic/backport-5.4/831-v5.9-usbip-tools-fix-build-error-for-multiple-definition.patch

@@ -0,0 +1,33 @@
+From d5efc2e6b98fe661dbd8dd0d5d5bfb961728e57a Mon Sep 17 00:00:00 2001
+From: Antonio Borneo <borneo.antonio@gmail.com>
+Date: Thu, 18 Jun 2020 02:08:44 +0200
+Subject: usbip: tools: fix build error for multiple definition
+
+With GCC 10, building usbip triggers error for multiple definition
+of 'udev_context', in:
+- libsrc/vhci_driver.c:18 and
+- libsrc/usbip_host_common.c:27.
+
+Declare as extern the definition in libsrc/usbip_host_common.c.
+
+Signed-off-by: Antonio Borneo <borneo.antonio@gmail.com>
+Acked-by: Shuah Khan <skhan@linuxfoundation.org>
+Link: https://lore.kernel.org/r/20200618000844.1048309-1-borneo.antonio@gmail.com
+Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
+---
+ tools/usb/usbip/libsrc/usbip_host_common.c | 2 +-
+ 1 file changed, 1 insertion(+), 1 deletion(-)
+
+(limited to 'tools/usb/usbip')
+
+--- a/tools/usb/usbip/libsrc/usbip_host_common.c
++++ b/tools/usb/usbip/libsrc/usbip_host_common.c
+@@ -23,7 +23,7 @@
+ #include "list.h"
+ #include "sysfs_utils.h"
+ 
+-struct udev *udev_context;
++extern struct udev *udev_context;
+ 
+ static int32_t read_attr_usbip_status(struct usbip_usb_device *udev)
+ {