Sometimes `make install` touches a file inside the build directory, so it is
betterr to create the build stamp after calling `make install` otherwise the
package is going to be rebuild even though nothing really changed.
git-svn-id: svn://svn.openwrt.org/openwrt/trunk@19021 3c298f89-4303-0410-b956-a3cf2f4a3e73