[IMP] Add a warning on UseOpenSSL script to avoid unwanted OpenSSL installation to be found

[lulivi]

System information

• Affected script: cmake/Modules/UseOpenSSL.cmake
• Affected repository:
• Operating system:
• Compiler:
• Compiler version:
• Additional information:

What is the current behavior?

When building a Connext example inside the rticonnextdds-examples repository, if the UseOpenSSL.cmake script is included before searching for the security plugins (and therefore for OpenSSL) in the FindRTIConnextDDS.cmake script, there is a special case that can happen:

• The CONNEXTDDS_OPENSSL_DIR CMake variable is set, and the OPENSSL_ROOT_DIR CMake variable is empty.
  This can happen and will yield to unexpected results, since the CONNEXTDDS_OPENSSL_DIR variable is not used in the UseOpenSSL script.

To avoid this, we can add a simple check:

if(DEFINED CONNEXTDDS_OPENSSL_DIR AND NOT DEFINED OPENSSL_ROOT_DIR)
    message(WARNING "Ensure you are searching for the security_plugins component of the FindRTIConnextDDS script when using the `CONNEXTDDS_OPENSSL_DIR` variable")
    set(OPENSSL_ROOT_DIR "${CONNEXTDDS_OPENSSL_DIR}")
endif()

Steps to reproduce the issue

Expected behavior

Suggested solutions