configure: Try to detect LZO with pkg-config

configure: Try to detect LZO with pkg-config

On most systems this should work just fine.

v2:
 - simplify code by removing -llzo special handling
v3:
 - reintroduce support for autodetection without pkg-config,
   no need to break backwards compatibility right now
v7:
 - Handle case correctly where lzo/lzo1x.h can not be included
   at all. On most distros this works even though the .pc
   file suggests to use it without. We had some partly
   solution for that but it wasn't really working.
v8:
 - Handle systems that do not implicitly include limits.h
   in configure test builds.
   lzodefs.h usually relies on lzoconf.h to include it.

Change-Id: I1c038dc4ec80d3499582d81eee61fee74f26e693
Signed-off-by: Frank Lichtenheld <frank@lichtenheld.com>
Acked-by: Gert Doering <gert@greenie.muc.de>
Message-Id: <20240626161921.179301-1-frank@lichtenheld.com>
URL: https://www.mail-archive.com/openvpn-devel@lists.sourceforge.net/msg28848.html
Signed-off-by: Gert Doering <gert@greenie.muc.de>