[ENH] Add support for QNX to resources/cmake/FindRTIConnextDDS.cmake

[grahonan]

Enhancement description

FindRTIConnextDDS.cmake does not currently accept QNX architectures for the CONNEXTDDS_ARCH variable. We can add QNX support on line 1131:

elseif(CONNEXTDDS_ARCH MATCHES "QNX")

    set(CONNEXTDDS_EXTERNAL_LIBS
        "-lm"
        "-lsocket"
    )

    set(CONNEXTDDS_COMPILE_DEFINITIONS
        "RTI_QNX"
    )

Once this is added, we can build for QNX like this:

cmake .. -DOPENSSL_ROOT_DIR=/home/dsuser/grayson/tmp/rti_connext_dds-6.1.1/third_party/openssl-1.1.1n/armv8QNX7.1qcc_gpp8.3.0/release -DCONNEXTDDS_DIR=/home/dsuser/grayson/tmp/rti_connext_dds-6.1.1 -DCONNEXTDDS_ARCH=armv8QNX7.1qcc_gpp8.3.0 -DCMAKE_C_COMPILER=qcc -DCMAKE_CXX_COMPILER=qcc -DCMAKE_CXX_FLAGS="-Vgcc/8.3.0,gcc_ntoaarch64le -Y_gpp -lang-c++"

cmake --build .