As of glibc 2.39, libdl.so and libutil.so are gone (they are part of
libc proper since 2.34), but empty .a files are provided for backward
compatibility with code using -ldl and -lutil. Keep them.
* guix/build/make-bootstrap.scm (make-stripped-libc)[%libc-object-files-rx]:
Mach libdl.a and libutil.a.
Change-Id: I967c6f34a443366224293362b8a2302fe86fd5a0