cmake HAVE_GSL examples

mysql/mysql-connector-cpp jdbc/extra/otel/opentelemetry-cpp-1.12.0/api/CMakeLists.txt :87 

target_compile_definitions(opentelemetry_api INTERFACE HAVE_GSL)

gnuradio/gnuradio gr-fec/python/fec/bindings/CMakeLists.txt :72 

target_compile_definitions(fec_python PUBLIC -DHAVE_GSL)