Disable warning to fix linux_netlink build

Change-Id: Ia759aa359c0fd14ad9ba15c5ad895741ff05052b
diff --git a/libusb.BUILD b/libusb.BUILD
index 07ba2d8..19d6984 100644
--- a/libusb.BUILD
+++ b/libusb.BUILD
@@ -169,6 +169,9 @@
         ":libusb_headers",
         ":libusb_posix",
     ],
+    # linux_netlink.c passes a buffer pointer (`unsigned char*`) to a function
+    # expecting `char*`.
+    copts = ["-Wno-pointer-sign"],
 )
 
 cc_library(