How to override external dependencies build flags?

[tsvi...@iota.org]

Hi, i'm building code that make use of an external dependency that treat warning as errors (--copt -Werror)
and i'm building with a crosstool that make use of different compiler thus results in warnings which fail the build
how can i override -Werror?

i'm building using this command:
bazel test --copt -Wno-error --crosstool_top=@iota_toolchains//tools/x86-64-core-i7--glibc--bleeding-edge-2018.07-1:toolchain --cpu=x86_64 --host_crosstool_top=@bazel_tools//tools/cpp:toolchain //common:common

this is the repo:

https://github.com/iotaledger/hub

thanks :)