git 2.50.0 was failing to build when libsysinfo was installed and, to
workaround this issue, an option LIBSYSINFO was added to the port and a
small change made on configure.ac to make it possible to disable this
knob.
After some discussion with git developers they prpoposed a different
approach to just ignore libsysinfo if it's installed because git should
never use it on FreeBSD. It should use BSD_SYSCTL option instead.
This change removes the LIBSYSINFO option and properly change
configure.ac to ignore LIBSYSINFO when HAVE_BSD_SYSCTL is set. This way
git will build exactly the same when libsysinfo is or not installed.
Obtained from: https://lore.kernel.org/git/b57b1418-2179-480c-92a3-a107388d71f2@gentoo.org/T/#ma65c83afdc1918ffdb18c9cae9ead29db4738b0f
Sponsored by: Rubicon Communications, LLC ("Netgate")
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