Fix libedit detection on *BSD OS's
Fix libedit detection on *BSD OS's

The following patch allows the autoconf script to detect the presence of
libedit when there isn't a pkg-config file present and thus allowing
Varnish to detect libedit on OpenBSD/FreeBSD/NetBSD/DragonFly.

Fixes: #1003

gauthier-delacroix/Varnish-Cache,zhoualbeart/Varnish-Cache,varnish/Varnish-Cache,gauthier-delacroix/Varnish-Cache,franciscovg/Varnish-Cache,chrismoulton/Varnish-Cache,feld/Varnish-Cache,alarky/varnish-cache-doc-ja,zhoualbeart/Varnish-Cache,franciscovg/Varnish-Cache,alarky/varnish-cache-doc-ja,franciscovg/Varnish-Cache,mrhmouse/Varnish-Cache,mrhmouse/Varnish-Cache,varnish/Varnish-Cache,mrhmouse/Varnish-Cache,feld/Varnish-Cache,chrismoulton/Varnish-Cache,ajasty-cavium/Varnish-Cache,1HLtd/Varnish-Cache,mrhmouse/Varnish-Cache,gquintard/Varnish-Cache,1HLtd/Varnish-Cache,alarky/varnish-cache-doc-ja,ajasty-cavium/Varnish-Cache,franciscovg/Varnish-Cache,varnish/Varnish-Cache,alarky/varnish-cache-doc-ja,franciscovg/Varnish-Cache,gauthier-delacroix/Varnish-Cache,ajasty-cavium/Varnish-Cache,1HLtd/Varnish-Cache,1HLtd/Varnish-Cache,feld/Varnish-Cache,gquintard/Varnish-Cache,zhoualbeart/Varnish-Cache,ajasty-cavium/Varnish-Cache,feld/Varnish-Cache,zhoualbeart/Varnish-Cache,feld/Varnish-Cache,gauthier-delacroix/Varnish-Cache,chrismoulton/Varnish-Cache,gquintard/Varnish-Cache,ajasty-cavium/Varnish-Cache,varnish/Varnish-Cache,alarky/varnish-cache-doc-ja,mrhmouse/Varnish-Cache,chrismoulton/Varnish-Cache,gquintard/Varnish-Cache,gauthier-delacroix/Varnish-Cache,zhoualbeart/Varnish-Cache,varnish/Varnish-Cache,chrismoulton/Varnish-Cache