This file is generated, so it should be referred to as
$(top_builddir)/src/gudev/gudevenumtypes.h. It could only appear in
$(top_srcdir) as a result of previous build in $(top_srcdir). Better
to just let automake add the prefix for us, so there's no need to
spell it out.
Remove the prefix from other source files too, $(top_srcdir) is the
default anyway.