package/flatcc: disable -Werror

package/flatcc: disable -Werror

Disable -Werror to fix the following build failure with gcc 11:

/data/buildroot-autobuilder/instance-0/output-1/build/host-flatcc-0.6.0/include/flatcc/reflection/flatbuffers_common_builder.h: In function 'flatbuffers_char_array_copy_from_pe':
/data/buildroot-autobuilder/instance-0/output-1/build/host-flatcc-0.6.0/include/flatcc/reflection/flatbuffers_common_builder.h:341:3: error: this 'for' clause does not guard... [-Werror=misleading-indentation]
  341 |   for (i = 0; i < n; ++i) N ## _copy_from_pe(&p[i], &p2[i]); return p; }\
      |   ^~~

An other option would have been to retrieve the following upstream
commit:
https://github.com/dvidelabs/flatcc/commit/f8c4140dd9dde61c86db751f6002def78754fced
but disabling -Werror is more future-proof

Fixes:
 - http://autobuild.buildroot.org/results/4d5cdddbfeefdeb943234b76eb08b04376f3c36d

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>