smtpping fails to resolve DNS on macOS

[zdAlexM]

Building smtpping with the GCD semaphore patch on modern macOS correctly initializes the semaphores, but name resolution is broken:

alex.maestas@RY624JJQPL:~/package/smtpping π clang++ -DBIND_8_COMPAT -lpthread -lresolv -o smtpping smtpping.cpp resolver.cpp
alex.maestas@RY624JJQPL:~/package/smtpping π ./smtpping -r -P 10 -s 102400 support@z3n-alexm-998.zendesk-staging.com
failed to resolve z3n-alexm-998.zendesk-staging.com
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