configure: another improvement in the libav detection, fixes #2382

configure

@@ -372,13 +372,14 @@ else
 
     if $has_libav; then
       enable libav
-    elif enabled_or_auto libav; then
-
-      die "libav development support not found
-(use --disable-libav or --enable-libffmpeg_static)
-((supported ffmpeg libs n1.2+))
-((supported libav  libs v10+))"
-
+    else
+      echo "WARNING: none or old libav or libffmpeg libraries were detected"
+      echo "         * use --disable-libav or --enable-libffmpeg_static"
+      echo "         ** supported ffmpeg libs n1.2+"
+      echo "         ** supported libav  libs v10+"
+      if enabled libav; then
+        die "libav development support not found"
+      fi
     fi
   fi
 

support/configure.inc

@@ -204,12 +204,15 @@ check_pkg ()
 
   printf "$TAB" "checking for pkg $pkg $ver ..."
 
+  dver=$(pkg-config --modversion $pkg 2> /dev/null)
+  test -z "$dver" && dver="<none>"
+
   # Check for package
   if pkg-config $pkg $cver; then
-    echo "ok"
+    echo "ok (detected ${dver})"
     enable_pkg $pkg
   else
-    echo "fail"
+    echo "fail (detected ${dver})"
     return 1
   fi
 }