macOS: Try to make sure we can find brotli.

libbrotlidec and libbrotlicommon show up in `otool -L` without any path
information on the macOS builders, similar to what's described at

https://github.com/google/brotli/issues/934

Try to work around this in osx-app.sh.

packaging/macosx/osx-app.sh.in

@@ -320,6 +320,17 @@ rpathify_file () {
 				echo "Changing reference to $dep_lib to $to in $1"
 				/usr/bin/install_name_tool -change "$dep_lib" "$to" "$1"
 			done
+
+			#
+			# Try to work around brotli's lack of a full path
+			# https://github.com/google/brotli/issues/934
+			#
+			otool -L "$1" | grep '^	libbrotli' | awk '{print $1}' | \
+			while read -r base ; do
+				to="@rpath/$base"
+				echo "Changing reference to $base to $to in $1"
+				/usr/bin/install_name_tool -change "$base" "$to" "$1"
+			done
 		fi
 
 		#