"make bzImage && sudo make install" had the problem that during
the "sudo make install" the build system would notice that the information
in include/linux/compile.h is not accurate (it says "compiled by <user>",
but we are root), thus causing compile.h to be updated and leading to
some recompiles.

We now only update "compile.h" if the current user is the owner of
include/linux/autoconf.h, i.e. the user who did the "make *config". So the
above sequence will correctly state "compiled by <user>".