Use $vfwcap_indev_extralibs variable instead of duplicating "-lvfw32" in

capCreateCaptureWindow() check.
Based on patch by kemuri <kemuri9 at gmail dot com>

Originally committed as revision 21409 to svn://svn.ffmpeg.org/ffmpeg/trunk

configure

@@ -2542,7 +2542,7 @@ check_header linux/videodev.h
 check_header linux/videodev2.h
 check_header sys/videoio.h
 
-check_func_headers "windows.h vfw.h" capCreateCaptureWindow -lvfw32
+check_func_headers "windows.h vfw.h" capCreateCaptureWindow "$vfwcap_indev_extralibs"
 
 # check for ioctl_meteor.h, ioctl_bt848.h and alternatives
 { check_header dev/bktr/ioctl_meteor.h &&