Expect the C runtime on Linux to always have getaddrinfo(), glibc 2.1
was released in 1999 so by now every Linux environment should have this
function. This enables use of getaddrinfo() on C libraries other than
glibc, i.e. on musl libc.
This is an alternative approach to the patch posted to the gkrellm
mailinglist by Felix Janda which unfortunately had some drawbacks on
other platforms that need additional includes or libs when using
getaddrinfo(), most notably Solaris and Windows.
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