Bug 3754: configure doesnt detect IPFilter 5.1.2 system headers

Bug 3754: configure doesnt detect IPFilter 5.1.2 system headers

Solaris 10+ bundles IPFilter code natively, but the IPFilter
headers contain a duplicate definition of minor_t which does
not match the existing OS definition.

The result is that no applications (such as Squid) will build
on Solaris with the natively provided headers.

Also, the upstream IPFilter code separate from Solaris contains
the same minor_t definition so building against a separate
install of IPFilter does not fix the issue.

We must instead play fancy games #define'ing minor_t to a
different real-name for the OS headers and its own name for
the IPFilter headers.

 Thanks to Yuri Voinov for sponsoring the Solaris 10
 machine and environment resources for this fix.