Link libfcgi.a when building with FastCGI

Patched `configure.ac` to find and link libfcgi.a statically.
Haven't worked with autoconf before, so I'm taking no responsibilities for this ;)

As far as I understand, with this `-l:libfcgi.a` notation it looks in any given `-L` locations.
I guess the other way would be to add another configure switch like `--fastcgi-lib=/usr/lib`.