bad: disable dtls test if openssl is not present
On MacOS with homebrew, the openssl library is not properly detected with pkg-config. So disable the test compilation if openssl is not properly detected along with libcrypto.
libcrypto is detected but it uses the system one which leads to the error:
your binary is not an allowed client of /usr/lib/libcrypto.dylib for architecture x86_64
See more details from Apple: