Remove -Werror

[AMDmi3]

-Werror should only be used in CI.

In particular, this breaks build on FreeBSD:

./bitstream/mpeg/psi/descriptors.h:78:24: error: variable length arrays in C++ are a Clang extension [-Werror,-Wvla-cxx-extension]
   78 |         char psz_value[2 * i_length + 1];
      |                        ^~~~~~~~~~~~~~~~

[AMDmi3]

Thanks!