GNU: Use -fvisibility on AIX when supported
Revise the logic from commit 4feba34d to add a version check. The GCC 7 release notes state that visibility support has been added for AIX 7.1 and above.
Revise the logic from commit 4feba34d to add a version check. The GCC 7 release notes state that visibility support has been added for AIX 7.1 and above.