Why we ever linking with flatbuffers compiler library???
On windows mingw platform all executables as a result will be flatc command line utils (((
Because flatbuffers target contains "main" function...

Fix it by not set FLATBUFFERS_LIBRARIES at all (because it header-only library!)
cmake: remove unneeded flatbuffers code... only FLATBUFFERS_INCLUDE_DIRS should be set (for now to our external/flatbuffers directory)
Merge pull request #9568 from vovkasm/pull/fix-cmake-link

cmake: fix tests linking